If youre talking about a 4 player match in general, its easy. Most 4 players matches are guests and low level players. What you need to know is never stay in the same spot for too long (snipers bomb. bomb. bomb. other abilities. u will be dead if you stay on the ground too long in the same place.).
Second, there are only a few things you needa know, i assume ur playing gunner. Few tips:
(1) fast killz - E + F + Assault Rifle (effective!)
(2) dont try sniping yet. effective, yes, but easy to master, no.
(3) so that goes to say just use Assault Rifle for now - does decent dmg. Pair with shatter bomb.
(4) goes for any hero- never throw a bomb too near. it will dmg u.
(5) try not to just walk around on the ground, use jetpack, jump over your enemy, etc...
OH and btw capture the control point. I've seen so many players just walking around chilling and killing but never capturing. Always try to capture except with bomber.