Heavy/Assault: You should be at the front line leading the charge. If you give any #@!&s whatsoever about your own safety you should play another class. Your goal is basically to roleplay an ork from Warhammer 40K. Leroy Jenkins is your spirit animal. Am I getting through here? 9 times out of 10 the more aggressive team wins. A unified push is literally all it takes to win at low tiers. Make sure your team knows they should get ready for a push, and if the other heavies and assaults follow you there's a 99% chance you'll absolutely curb stomp the enemy team.
Medium: Your job is fire support. Stay behind the heavies and shoot what they shoot. Keep an eye out for flanking lights and deal with them before they have a field day with the backs of your assaults.
Light: You have the most complicated role. In domination you should be the first person into the yellow circle and stay in it until your team catches up.
In conquest your job is to run around and cap bases.
In assault you should be the first responder if the enemy starts capping your base. Even if you can't kill them, you can at least pop out of cover once in a while and shoot them so they can't cap. Shooting an enemy stops the cap for a few seconds.
In skirmish it's your job to locate the enemy force at the beginning of the game. This is a scouting job only. If you try to take them on without your team you're going to have a bad time.
Light mech combat tips: Never stop moving. Don't go below 100% throttle unless you really, really need to. Never travel in a straight line. Some big mech with gauss, AC20, PPC or whatever can easily one shot you if you let him lead his shot. You don't have much firepower so make it count. Hit R to target the enemy. This does two things. The first is that it lets you see where the enemy is already damaged so you can shoot them where they're weak. You don't need big guns to blow up a half dead body part. The second reason is that you'll be a spotter for LRMs. Use your speed to your advantage. Mechs are much less armored on the rear torsos. Your speed makes it easy for you to flank a mech that's fighting one of your larger friends. Finally, being a light means you almost never have to stay in an uneven fight. If you're at a disadvantage it's usually pretty easy for you to just run away, preferably while putting as many objects and pieces of terrain as possible between you and your pursuer.
I really doubt the potatoes in question read the forums, but hopefully this helps someone out there.
Edited by Plaid Ninja, 20 February 2018 - 09:12 PM.