Caution. That is what you need to exercise. I'm not claiming to be a a pro, actually I'm a new player. But from my experiences, just leave players alone. I've noticed players about, that haven't seen me, and have just kept an eye on them and as soon as they pass, I start moving again. There are friendlies, I'm sure, but there is the worry of you killing them. People say friendly, and then shot you in the back some times. You have to get into the mindset that this isn't a co-op game, it's a survival game. Sure, joining up increases survival, but some times staying a lone and shooting a player that MAY be your downfall will keep you surviving longer. Just don't draw attention to yourself. Don't linger anywhere. Sneak, get your stuff and then get out of there as fast as you can. If your gunfire is attracting people, then you need to train your trigger finger to only shoot when you need to and avoid shooting.