All I can say is be a city elf. Be a dick to everyone. Win.

I don't think this would be a good game to rent.  I like to play as a mage too by the way, i found it more interactive for my own character which i control most battles.

Make everyone in your party a healing mage and then dance around in the horde of dark spawn.

Playing through each origin story will give you a lot more information and flesh out certain characters you might otherwise see as throwaway ones.
 
If you're playing the 360 version, play on easy. If you're playing the PC version (I'd assume not with the "rent" statement) play on normal.
 
Mages are fun and the right build can be overpowered compared to other classes.
 
Buy every "backpack" you can find as soon as you can (they increase the maximum amount of items you can carry). You might not be able to get some of the earlier ones later.
 
Pickpocketing every single character you meet will net you a ton of useful gold and items by the end of the game. Each single person might not have a lot, but money is somewhat scarce in Dragon Age, and every little bit adds up.  On that note, horde every item you can, even if you don't intend on using it, and sell it back at a town.
 
As annoying as it can be, always have a rogue in your party, and one with high cunning/lockpicking/pickpocket ability. There's no bashing locks to open them, and the items you can find in some of the higher difficulty chests can often be worth it. Also, you'll be able to see and disarm annoying traps.
 
Learn spell combos and use them often.

If you care more about min/maxing then keeping to some sort of story figure. I would make your character a Mage spec'd for Blood Magic/Arcane Warrior and Spirit Healer since you get one "pure" healer in the game and they can come late depending how you go about doing the story line, use the other characters for your warrior/rogue/damage dealing mage needs.
 
Mage is probably the most fun class I played(beat it three times on PC as each class). Lots of of fun to Storm Of The Century an entire room of mobs.
IIRC friendly fire isnt turned on on the console game, so feel free to drop AoEs on your own guys if you need to.
Winter's Grasp is fucking amazing, as is Cone of Cold.
 
As you might guess most of my experience comes from playing as a Mage, but Dual Wield Warrior was alot a blast watching all the white numbers pop up.

I played all the Origins stories, and I found the Dwarf Noble to be the most engaging. The other ones are all kind of predictable and generic but for some reason, I felt like they put a lot of work into the Dwarf Noble. 
 
It was also my favorite part of the game as a whole, which is a shame because Dwarf Noble was the first one I picked. So I was done with the best part of the game at the beginning :( But don't go in expecting an absolutely epic story... the story in Dragon Age is... well, I guess you could call it "humble". Some would call it generic and unoriginal as well. The universe is also not as engaging as, say, Bioware's OTHER rpg series... :P 
 
But if you like a KOTOR style gameplay, Dragon Age is your only choice.

If you want your main character to be controlled the most, be a mage. About halfway through the game you'll be relying on your mage more than any other characters. So that mage might as well be yours

I'd actually recommend Gameflying it, if you have that option, especially if you can get it without too long of a wait. 
 
I made the mistake of buying the game, since I love RPGs and I heard so many great things about the game.  It just...wasn't for me.  I could give plenty of reasons why, but in the end it's something I wish somebody had told me "rent, don't buy" instead of all the recommendations to just buy it straight out.   Also, I'd advise against trying Rogue as your first class, by far the most boring and lacking in options compared to the others.  Probably try Mage, they have by far the most options in different situations, and more than 1 or 2 useful abilities.  
 
As you said, if you like it you can always keep it, and still end up saving money, so I'd say Gamefly is the way to go.

I think dragon age is the best game of last year

" Awesome.  Sounds like I'll be making a mage then.  The mage class isn't usually the way I go in games so it'll be interesting to see how this works out.  And yes I'll be gameflying it just in case.  Thanks again. "

I've played through the game a couple times, I really think its over-hyped. Don't get me wrong, its not a bad game, but everything about it seems so bland. The plot was very thin, you don't know much about your enemy and why they want to kill mankind. The combat was dull, walk up press X, Y, B in order, wait for your spell cooldowns to finish. Repeat. I also hate the silent main character. Sure you talk through text options, but having your main character have no actual audible voice just seems to separate me from the character which makes it hard to get into the experience of the game. The supporting cast voice-overs were good, and their back stories and involvement in the game are very cool (Morrigan was awesome). I found doing a lot of the side-quests was annoying as most of them are pointless and don't really progress any plot points. It was just one of those games where once I get about half-way or three-quarters the way through I just stop caring about whats going on and I want to finish it and pick up a couple achievements. It dragged on, I'm trying not to spoil anything but basically your trying to unite factions against your enemy. But as luck would have it, each faction has its own problem they look to your to solve before they want to give you a hand. It made the game drag on.
 
The system they set up where your choices effect the game was very well done I thought, it was probably the best part of the game. But I found that it didnt matter if your character was nice or a complete dick and there is no good/evil type thing.

I know it seems Im knocking the game, but I really didnt think it deserved the reviews it got. I'm really surprise at how many people say this was the best game of '09. I'm a pretty big RPG fan, but this one just seemed to sterile to me. Its just one of those games that once you finish you go wow, that could have been way better.
 
Personally, its hard to recommend this game to somebody when theres other really great RPGs out there. Mass Effect 2, Fallout, Final Fantasy 13 in a couple weeks. I'd spend the money on those over this game.

mages are fucking over-powered. 
 
But this game is awesome, I played through it once, and I wish I could find the time to play it again.

If you're not going to play as a healer, go to the Circle of Magi first thing.