I'm having a blast playing the multiplayer so I'd thought I'd share some of the few tips I've learned over my 20 levels of play so far. If you have any tips or tricks feel free to share. 
 
MODE: Wanted 
I'm not great at this mode, but I'm not terrible either. I'm not sure if running around on the roof tops works better or walking along the streets is the way to go. It depends on the map in some regard, but I think that moving along the rooftops is a better way to spot the people hunting you.   
 
Abilities: Smoke is a must. Disguise and morph are also important although if I had to choose I would pick Morph. For the larger maps you might want some kind ranged weapon or sprint to close the distance. 
 
Streak bonuses: I go with the +100 streak bonus because I find it tough to get silent kills. On the loss streak I go with ability cool down. 
 
MODE: Manhunt 
I love this mode. For those just starting out Manhunt offers some of the best XP per game. It's also nice having one whole turn to hunt and one whole turn to hide. i think the big trick to these is to hunt and hide in packs. Stick close to your teammates - not only do you get a bonus when hiding you also get bonuses when killing. 
 
Abilities: When hiding I use smoke and morph. A fun little trick is to find a pack of NPC next to a hay bale, morph them to look like you and then hide in the hay bale. Most of the time the hunters take the bait and you can jump out and stun your pursuer. Another fun trick is to get your buddy and chain stun a hunter till he has to respawn.  On the hunting side I use morph and firecracker. When approaching a group of targets, through down your firecracker and the player will be the only one that doesn't cringe in fear.  
 
Streak bonuses: I go for the 300+ bonus because it's easier to get silent kills in this mode. For the loss streak I still pick Ability cooldown 
 
MODE: Alliance 
I'm not sure how I feel about this mode. I don't play it a whole lot, but from what little I've experienced it's better when you stick by you partner. You can kill targets easier and you can cover each other's backs when attacked. 
 
Abilities: I go with smoke and firecracker. One to break pursuit  and one to smoke out your targets. 
 
Streak bonuses: 300+ streak bonus and Ability cool down 
 
MODE Advanced Wanted 
I absolutely suck at this mode. If any one has any I'd love to hear them. Also I haven't unlocked perks yet so if anyone has any tips on those I'd love to hear them. 

i really hate people that stay on the roofs the entire time in wanted.  Makes it not very fun imo.  Part of the game tho.  
 
I suck aat Advanced Wanted as well.  Seems like people are more inclined to stay on the rooftops even more-so in that mode since the indicator doesn't tell you if they are on the ground or not.  Half the time I get near an enemy and can't locate them because the indicator is so vague in that game mode.  And I swear when I get to my target there are like 5-6 NPCs of that same guy standing around yet I look around and never see more than 1 or 2 duplicates of my character.  The game is out to hate me I tell ya!
 
I feel like there needs to be something you can do more defensively.  I can see a guy coming at me that is going to assassinate me and it won't allow me to stun him which is annoying.  My inclination is to stay and fight them and not run but I guess I need to just start running which lets them know I'm their target tho....

also, the Gun seems to work pretty good for other people  but I can't figure it out.  I lock onto targets and get a LOCK symbol all the time.  Seems like I can't assassinate them.

Well I finally hit 50 so I thought I would share a few more thoughts and tips for anybody out there enjoying the multiplayer. 
 
I mostly play Manhunt , so the following are tips just for that mode. 
 
• Smoke Grenades are king - I can't stress enough how important the smoke grenades are in Manhunt. As you go up in levels and complete the challenges you get smoke grenades that have a larger range, smoke that lasts longer and smoke grenades that have a faster cooldown. Personally I like the grenades that have the longer range. When you have a hunter creeping up on you they like to  try to hang just on the edge of where your smoke might hit them - trying to get you to throw it down with out them being affected. With the longer range you get the creepers hacking up smoke while you punch them in the face. 
 
• Charge is awesome in defense - The best thing about charge is that you can rush at a hunter and stun them. Sometimes it's a little janky,  but if you catch a hunter alone, lock onto him or her and use the ability to run up to them and get a stun. On the flip side if you see  player charging at you, throw a knife, it counteracts the charge so you can get in close for the kill. 
 
• Use blend and quick escape for your perks - The blend perk is great because it  basically acts like a mini morph. Every time you join a crowd one of the character types changes to look like your avatar. Quick escape makes your escape meter run down quicker. Once you break line of sight and blend with the crowd it counts down super fast and unless your pursuer is right behind you, you can almost always escape. 
 
• Don't be afraid to run - If you see a hunter coming up on your position, you can try to stick around and stun them with a smoke grenade, but it's far better to just book it. If I'm hiding in a group and I see the hunter use Templar vision, I almost always make a run for it.  If you get them to chase you, it's easier to loose them in the crowd than it is to try and stun them.

Those are some really good tips and manhunt is by far the best mode.  I think the freeLC is including an advanced manhunt.  
 
Manhunt -  general tip do not pick a character that stands out from a distance i.e. the harlequins and the blacksmith.  you can see them coming from across the level.
 
Offensive/Killing side - You need Templar Vision.  The real player has a blue aura when you use this mode and you can pick them out of a morphed crowd far easier than waiting to see if a player acts weird.  Plus by the time you actually pick them out they've probably noticed you and you'll have smoke in your lungs and a stun coming.  Definitely stay in a pack to kill.  If the other team has a lot of smoke bombs your buddy can kill the dude if you get stunned.  Poison is a great way to rack up the points as well.  Wait for a buddy to charge a target, let them get smoked and then poison the player that stuns them.  this adds an automatic +200 and is really easy to do.  Another poison tip is to equip Disguise along with it so the target doesn't realize it's you.
 
Defensive/Hiding side -  Sticking together not only increases points when all players are hidden you can also help each other by smoking the attackers.  And unlike Wanted stunning does not "cancel" you from being a target.  It does until the stunned player stands up again so after a stun, RUN.  and remember the attackers buddy could be right behind him so plan your smokes and stuns appropriately.  Recommend Smoke and Mute for this half of the match.  Mute is really good when the attacker has Charge going not only does it cancel the charge it leaves them vulnerable for that 1.5 seconds, so be quick with the stun.
 
Since peeps be having trouble with advanced wanted
 
Advanced Wanted - general tip BLEND.  Always be in low profile on the ground.  And change planes, being on the roof is more effective in this mode
 
To Kill peeps - Templar Vision is very useful.  If you are against that strategy then notice little oddities in morphed crowds.  remember the target will never be at the lead of a morphed group and look for one of them running into another, that's a key give away that its a player not an NPC.  also there are certain paths that NPC do not take such as the chase breaker gates.  if you see a character walking between the glowing gates it's a player so run or kill them depending.  Knives and Guns are good abilities to have.  Knives can knock down a player if they are looking over the edge of a wall or running up a wall while causing them to limp around.  Easy to pick em off if you're in the right position. 

I mostly use smoke and morph on each game mode, useful for everything I think. There are times though when I see someone I need to kill running about like a madman and I just can't catch them, the gun would be helpful there.

I still don't understand how Stun works.  It feels like it randomly works every 5th time I try it.  I can see who is coming for me and when I'm trying to stun I get killed, even if I mash the button or hold it or try to time it, it never seems to work.  It just feels like there's something not explained in how it works and it's damn frustrating.

One tip I have, and it's pretty basic - remember that holding down the X/A button makes you walk faster.  It's not necessarily something you want to use all the time, but if you've found your target and you're trying to creep up on them, remember that you can walk faster.  It seems really simple but one of my friends constantly forgets about it/doesn't like using it and I often see times when he loses out on kills because he refused/forgot that he can walk faster without going high profile.
 
Another tip I can think of for Manhunt is that when you're hiding - don't panic.  It's really easy to mistake a hunter bluffing/thinking that they might know where you are for them actually knowing where you are, and panicking can end up getting you killed just as easy as playing it cool can.  Also, if you see a hunter going for one of your allies and you think you can get over and stun them before they kill your ally, do it.  Yes it will tell that hunter and all other hunters in the area that you're a player, and yes you will need to run after you do it, but it helps a lot.
 
One question I have though; how do people feel about Decoy in Manhunt?  I've used it a couple of times and have found it somewhat useful, but I'm honestly not sure if it's been any more useful than what any of the other defensive tools would have been.  Has anyone else given it a try?  I haven't really seen anyone recommending it, so I'm kind of curious if it's just a preference thing or if it's just too iffy compared to other defensive abilities, etc.

Can someone tell me how I stay in hiding places for the blue stay hidden timer, I always jump straight back out whether I press something or not.

Today i was sitting on a bench in wanted next to a likeness...i had two pursuers on me and i watched as one of them killed my innocent twin, THEN my target just happened to walk right into my blade as i set up and turned the corner. When moment like this happen, the game is magic. 
 
my tip is, if you have three pursuers, yer better off running on the rooftops to force them to reveal themselves. 
 
I've only played wanted so far...played one with three teams of two people each, guy bailed on me and i thought that mode sucked.

Tips for outsmarting your pursuers:

1. Watch for people who are fast walking in your direction - that's most likely your pursuer.  Either run or use an ability to set up a stun.
2. The best ability to stun others is charge.  If you know who your pursuer is, just charge toward him and you'll automatically stun them when you get close.  Mute is probably second best, but once you use it you gotta run at the pursuer since the duration is like 1.5 secs.  Smoke bombs are okay, but I don't like how close you have to get for them to be effective.
3. Something I like to do is look for a couple of my clones near a haystack/bush/etc, and hide in that.  Most of the time they will kill the clone.
4. You can also throw smoke bombs from inside a haystack, which is great for luring people into a stun-trap.
5. If you are in a chase, once you get some distance from your pursuer, go into a hiding place (group, haystack, bench).  The bar goes down a lot quicker and won't refill even if you are in their line of sight.
   

Im really good for some reason...top 3 all the games I've played. basic tips: Don't run unless the other guy is running/you're spotted. You don't know if anyone is watching to kill you, so even if you think you'll be safe you may not be. 
Look around you every few seconds...unless you're blending keep your distance from everyone else. If someone appears to be approaching you run through a gate or get on a roof...if they follow you up then you'll know that you should just run away. 
Above all, be patient. Wait for the kill in an isolated area if possible, definitely silent unless a chase.

So I just unlocked the firecrackers and noticed that nobody ever uses them.
 
Are they useful? I mean it seems like something that could come in handy while playing manhunt and weed the dude out of the crowds when he's blending in, but other than that it just seems like a giant siren for your character.
 
One of the many things I love about multiplayer is the fact that some of the mechanics you wouldn't expect to work in an online setting actually work amazingly well. I never thought hiding in a haystack from your pursuer would be one of these things that just amaze me every time it totally works.
 
Of course there are times when your pursuer dives right in after you and drags your limp body out.
 
Seriously, Ubisoft did something right with this stuff.

My list of tips: 

1. Lock your target. It makes a world of difference. You can also use the advanced lock by holding down the lock button.
2. Run, don't stun! If you see the red diamond, take note of that person's model (smuggler, priest, etc.), then flee. If you get away but don't trigger a chase, make sure THAT SPECIFIC MODEL never gets near you. You know what your killer looks like, now just look for him in the crowd.
3. If you must stun, be careful. Always stun from behind if possible, and use an ability (smoke bomb, firecrackers) if possible to make stunning easier.
4. Target on the roof? Climb to the ledge and wait. If you dangle from a ledge under your target, you can still get stealth kills on them. Lock them if possible, then just toss them to the street below and get tons of points.
5. If you're in first, just wait for points. Don't go out looking for them; if you hide/escape well, you will get all sorts of bonuses for just surviving.