Always review your gameplay. Watch some of your matches in theater find the mistakes you’re making and watch how other players are killing you. If you just finished a match where someone went 25-4 watch how they played. Also youtube is your friend!
Know the maps!!! Take time to learn each map, learn spawn points, and learn where people camp so you can avoid those areas.
Keep a cool head. If you rage at every single one of your deaths, then your performance is almost guaranteed to take a nosedive.
Play with a team or at least with a lobby that uses headsets. Communication is the key here. Call out campers and hope other teammates return the favor.
Use a weapon you’re comfortable with!! Don’t decide to try the weapon out to see if you like against other players.
Get a quality headset.. This will improve communication and allow you to hear what’s going on around you. I have some links on the right-side for headsets check it out and find what works best for you.