Don’t worry about K/D or win/loss ratio. If the guys you’re playing with care, don’t play with them
Seriously, it’s not worth it.
Biggest thing I would say is try and work on your movement. CoD is obviously pretty unrealistic, so don’t move like a real soldier would. Slid and jump a lot.
Second, what’s your loadout? That’s pretty important, you can only really use like 3 or 4 guns if you want to do well. If your BIL is good, he’ll probably know what guns to use. I haven’t played Warzone in awhile, so I don’t know what they are right now.