Aiming is maybe 40% of the game. You just have to play smart. If you had someone teach you you'd have been a great player. As long as you can kill somebody that isn't looking at you then you have great potential! Use your brain!
Camping is one of the easier ways, very effective especially in pubs. Learn to position yourself, people will just come into your crosshair! Using sound helps immensely, just prefire away. Flashbangs are extremely effective, use them to take ground or flash a camper. Nades are for flushing campers or stopping rushers. Know the map and its hotspots, you can wall people or know where to position yourself so people will run into your crosshair.
Ever remember that one guy in game who has like 30-4? All he did was master all the things I mentioned.