"Don't take the fight if you don't have to."
This is a phrase I find myself using to my teammates because they are kill hungry (Especially if their gear took control of them and made them think that they are invincible) and ultimately get 7.62 PS'd in the face or some shit. What I'm trying to say is that it is best to leave some enemies alone and retreat is the more sensible option.
If you don't know where your teammates are calling out the enemy, do this foolproof technique called "looking at where your teammates are pointing at".
Self explanatory, works best in duos/trios, not so much in quads or five-stacks. It is a more quicker way than the compass, but may not be reliable because you may not always have a line of sight on your teammate.
What ammo is in this mag?
You've seen streamers do this. Checking what ammo the mag has by double clicking it, and dragging it so that you can see the bullet and identify it by its tip. Requires practice and time in raid, here are some examples: 762×39 BP has a small black tip compared to PS (no tip). M61 has a black tip, m62 has a faded red tip, M993 has long black tip. Some ammo like 9×19 can be easily distinguished bc of their clear differences, while other ammo can be.. not so much (5.56)
Rebinding your discard key
The default key is del, a key that is pretty far away for your fingers to reach. I personally rebound my key to "z", but if you tend to fat finger often, maybe rebind it to keys like h or something. Rebinding it is very important, for it reduces looting time with the right click and discard when you can simply hover your mouse over the useless item and press z. With this, you can quickly do things like ditching your "rat rig" for a better piece of gear or anything like that.
This is all the tips I can really think of, might add more later.