I'll start by saying in this post I am not trying to brag, I've simply noticed a lot of players are TERRIBLE at the melee online. I played a few games of annihilation tonight and in every match had atleast 1/3rd of my teams kills as an assault marine/raptor.
First off, its really....simple. I still use a chainsword and bolt pistol despite having unlocked the thunder hammer, I've got enough kills with both to unlock the extended pistol mags and vamp for chainsword. Before this I used furious charge, the best alternative when unlocked is the revenge pack (although many players are starting to wise up to your leaving gift, it works about 10% of the time). Combat stim should be a no brainer, this is equipment made for the class, you can pop it in the air and should, before rushing down and landing on someones head in bloody combat.
The second and I think most important point is using your bolt pistol...thats right...the tiny little 'handgun' you're carrying? Its a magnum that can 1 shot unarmoured opponents, if you hit them in the face anyway. I have beaten tacticals using bolters, stalker bolters...even plasma rifles with this baby and it is so underused its almost a crime. Yes its accuracy when out of aiming mode is pretty meh, yes without a perk its ammo is terrible, but its damage is always solid. If you're running headlong into combat with a full clip against someone who is simply gunning you down, you should seriously be asking yourself why you're not atleast chipping at the guys armour before you either die or get that jump off that'll throw the advantage to you. Once again, use your bolt pistol, the plasma pistol is nice, but too easily avoided.
The third and final thing, yes, you can jump, yes, its sweet and awesome, no, its not for travel. Your jump is limited and precious, save it. At the start of a match its fine to blaze ahead to capture a point or scout out your first target, but after that use it with caution. If you get caught by a tactical without a jump, you're boned, if you get targeted by a devestator....you've got next to no chance. Also bare in mind that as well as an initiation, its a breaker, players will generally find it awkward to track you after a jump so you'll have a second or two of respite, this is where you need to make the snap judgement. Do you dive back in to stun them and get maybe 2 hits off before they lay into you again? Or do you duck over the wall and hope that you dont get spotted or naded? Most of the time, a mid-fight dive will push the fight heavily in your favour, especially with chainsword lifesteal, and net you an easy kill.
The only other thing I can think of is...ignore interrupt attacks, the animation takes too long and does too little to justify itself, I'm sure on other classes they work but for someone carrying a big melee weapon, a shoulder/stomp isn't going to effect them as much as 3 or 4 slashes as you dance around them.
I hope this helps anyone who finds the melee in the game lacking, the truth is, melee by itself IS lacking, its weak, taking around 4 solid hits on a target to down them unless you're using a perked thunder hammer in which case its only 1, but harder to hit. The melee classes carry a sidearm for a reason, they also rely a lot more heavily on messing with your opponent in terms of environment and engagement.
As for me, I've yet to get any 'decent' games under my wing as tactical or devestator, so feel free to do something similar to this for other classes, or tell me why I'm wrong about melee. All I know is the scoreboard doesn't lie, since pimping my pistol, stuff has gotten crazy.