Step one chossing your character and know its limit and strength 

if you choose carl then  this character is all about speed you need to max his dash lvl 3 and any equip that can bosst your speed and if your lacking grenade do quest  nothing more i can say to this character since i dont play him very often

burton now this character is more like a tank put some pure defend gear on this bad boy and badass rocket laucher every noob you play will yell RL noob but that his main point burton is heavy type  

Ai dont know about her but i dont play her as well but i know want this i like her cloack skill or shadow skill i dont what is called but i pretty useful and situation 

Marie dont know much but i prerty rough say she more of a sniper since i saw alot of player use her mainly of her sniping ability