Bloody hopeless at MP. Getting smashed every game. Kinda takes the fun out of it.
Semi auto rifle (with silencer upgrade), revolver, reviver (highest level) and healer (highest level possible)
Semi auto rifle (with silencer upgrade), revolver, crafter (highest level), reviver (highest level possible)
They're the two classes I run with whilst trying to up my population. Only use the good boosters when you have missions to complete. Use the more useless ones which you have multiples of in-between.
At the start of each round I rush 2 tool boxes and take up position at the 2nd one and just craft and kill the enemy. If you're on crafter you may be better off just trying to visit all of the tool boxes asap.
Go slowly and try and stay around enemy tool box areas hidden behind whatever you can find and wait for them. Always place a bomb (press R1) behind you if you have one so that they can't flank.
Molotovs are extremely useful for the camping method.
Don't underestimate the importance of smoke bombs and shivs.
Do the 400 rifle upgrade first, then get body armour (after initially upgrading your rifle try to get body armour each round if its degraded), then get the 800 rifle upgrade. It's always good to sometimes buy some ammo, especially if your teams getting hammered.
If your team is not great you want to stay 'near them' but don't bunch up with them. Either hang back or stay on the flank. Never be in front of them. That's the best way to stay alive.
Only go for the special execution (triangle when standing above a downed enemy) if you know no one else is around. Otherwise just use your weapon from afar to kill them.
Knowing the enemy tool box locations is the biggest tip probably (they don't show up for on the map).