The best help I can give you is some helpful advise. Ignore anyone who tells you to play on lost platoon. Unless you have a super organised team it's solid. Far better is to play on a small map like Alpha site, which requires less complex strategy.
I got endure on my first attempt on alpha site, with two other players who are mediocre at best and a 4th who was AFK for the majority of the match. I think we had something like 4 lives spare by the end of set 4 and only went down to the last man standing once.