On round one your going to wanna get as many points as you can. (Tip: on the first round i it takes 5 shots to kill then so try shooting them4 times then melee them.) You probably wanna get to the exo room as quick as possible. The first doors both the one leading to the decontamination and the hub costs 750 credits. Then after that the next 1000. But what i do after i run out if ammo on my Atlas 45 i buy the Mk-14 its a good gun to rack up points with. And of course you wanna get perks and upgrade your guns. But after about round 7 or 8 just trade it in for something better.
