There are only 7 Campaign missions, they are all pretty short and have a lot of checkpoints to help you get through them. Stick to cover and replenish your ammo every time you get the chance. There’s not much else you can do but to go slow, stay behind cover and take advantage of your grenades and other explosives.
Your teammates will kill some enemies but don’t rely on them to much as they will sometimes run right past an enemy or let enemies run behind them.
One thing you do have to watch out for are grenandes. It seems as if the enemies were all trained how to throw by Peyton Manning. They will throw a ton of grenades at you and they will always land right where you are standing no matter how far away you are or at what angle you’re at on hills.
If you attempt this first all of the other difficulty and completion achievements will pop once you beat all 7 missions.