My tactic is - I'm shit and will get owned in a fair 1 on 1 so I work out where enemy players are then get behind them rush up as fast as I can to take as many as possible by surprise then run away before reinforcements come, repeat. Or my local site has a great room were you can see the two ways in without the opposing team seeing you and no one bothers looking left/right so double tap to the side every time.
Wear full black kit with a climbing harness and abseil down into windows shoot everyone get shot in the leg a million times, don't call it and carry on