The most important tip I can give you is NEVER EVER SET UP OVER COVER. Never set up in a window, or on a low wall. You'll get shot instantly. You can't avoid enemies like the other classes can. Not only that, you're a very high priority target.
I disagree. Think outside the box. The cover mechanic is good if you use it differently to how just about everyone thinks. Imagine a situation where there is a single room building and the enemy are on the other side of it. Everyone I see runs into the building, sets up in a window facing the enemy, and dies.
What you should be doing is staying outside the building, setting up in a window on the far side from the enemy, facing into the building, and shoot through the windows on the other side. If no moron is in those windows, you can cover all of them without moving, and the enemy isn't sure where you actually are. If they try to grenade you, the room protects you. If they try to assault the room, you can still kill them without moving, or are free to move away from the building, or even hit space and be in the building pretty rapidly.
This is the way I use the cover mechanic. Not on the first layer of cover on this side of 'no man's land' but on the second or third layer, shooting over the top of the first. This means I can cover more of the frontage and be less visible and outside grenade range.
Still, never is better than bad, so don't use it unless it's a situation like this that can have it work out.
Conceal yourself as much as possible. Don't get seen, and don't fire unnecessarily.
But don't be too afraid to recon by fire. Fire a burst at a likely hiding place and see if anyone moves or tries to shoot back. Sometimes a sneaky bugger is crawling around thinking you have no idea he is there, but a random burst nearby gets him to stand up and run, thinking you know exactly where he is.
In this case you are intentionally setting yourself up as bait. You are in a position so that you can engage anyone who tries to come looking for you, so that is what you want them to do. You might also slow down an attack, simply by distracting it and turning it into an attack on you instead of the objective, making them waste lives pointlessly.
Don't stay stationary, crawl whenever you can, avoid sprinting or running, as this will draw attention.
Same as above, plus once you are in combat, and they know where you are, you should be moving from cover to cover as fast as possible, while trying to stay as concealed as possible. The more times you move between shots, the less knowledge about your location the enemy has, and the slower he has to go. If he knows where you are, and you don't move, he can get into dead ground and sprint around you before you even realise it.
Fire the burst, make him duck, then run and hide before he looks again. Use the sprint from prone so that all you have to do is let go of the keyboard, and the gun will eventually be properly deployed ready to fire. That has saved my life many times.
They key is to run just as far as you think you can before he can shoot at you. If he has a bolt action, you have a lot of time between shots to move, and once you're moving you're harder to hit. It's the getting up and going that gets you killed, not the running itself, if you don't run too long.
This is also how you train your enemy. You fire short bursts at random intervals only at known targets. Eventually, the enemy thinks that any time he moves, you will shoot at him, because he can't tell when you're moving, or reloading, or even if you can see him at that moment. He may even just hunker down and hope you move off. Basically you are shutting down his options until the only options left are suicidal. Then you can do pretty much anything you want. I have had guys so scared of me, that I casually got up and ran over to their cover and shot them, because they wouldn't even risk sticking their head up to look.
Battles are won and lost in the mind, long before they are won or lost on the battlefield. Knowledge is power, so what you are trying to do is get more power for yourself, and less power for the enemy. The less he knows about what you are doing and where, the harder it is for him to kill you. The more you know about what he is doing and where, the easier it is for you to kill him.
Of course, most of this isn't MG specific. You just have to modify the rules slightly to accommodate different weapons.
There are some specific MG tips that are the opposite of what you do with other weapons. For example where you aim. With any other weapon, you maximise your chance of neutralising the enemy if you aim at centre mass. By this, I mean the hips, rather than the chest. With the MG, you maximise your chances of neutralising the enemy if you walk your rounds onto the target rather than off, so your aim point should be much lower, say the knees or even the feet. That first round will hit the knees or feet, but the rest of the rounds will have a better chance of hitting the body and head.
There are more, but I'll stop here and let someone else have a go
I'm sure there are more tips I can give, but that's a good start.
There is so much we can all share. This is the kind of stuff I like to talk about, not "balance" or "bugs" or "nerfing". None of those things make as much difference as the tactics you use. The more we all share about them, the more fun we'll all have playing.
