Most of the tips you'd need to be aware of in advance are for the campaign. Make use of cover when you can find any, and don't forget that your allies can probably take care of some enemies for you. In some cases, enemies might spawn infinitely until you progress, but situations like these will be noted when they appear. It'd also be wise to conserve as much ammo as possible, which ties into letting your allies do some work for you.
The multiplayer grind is pretty daunting until you start to work on it. You do need eight people minimum to start a match, but if you do find a good set of people to boost with, it definitely shouldn't take more than ten sessions (of three hours each) to finish everything. There's no way you're going to be able to play a legitimate game of multiplayer anymore; whenever TA boosters are in the lobbies, they're usually the only eight people playing the game at that time.
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