Play DM, a lot... DM is a great way to improve accuracy. Just DM every day for an hour and listen to some music and I am sure you will see a great improvement in accuracy. A lot of pros do it and recommend it, I cant DM with my PC because it blows and lags too much, but I am planning on doing it once I get a new rig. Good luck man. There are also bot aim maps, but I don't really suggest those, considering the bots stand still or move in the same pattern every time.

I would recommend setting up your accuracy properly.



This video will show you how to find your perfect sensitivity.

As a rough guide, you shouldn't have it any higher than turning a full circle in one full mouse movement. i.e. moving your mouse from one side of your deskspace to the other should turn your player 360 degrees in game.
I use a 1.75 sensitivity (800 dpi) and I'm currently ranked at DMG.
I'm more about the surfing game than competitive though

Other than that, practice, practice, practice...

It really is one thing that gets better as you practise, I would just play DM and move on to Competitive when you feel confident enough and when your accuracy is good enough to play well with a team.

I used maps from the workshop to improve my accuracy, you could also play Deathmatch or Casuals for about half an hour or so each day and you'll start to see a difference. I've seen major improvements since using Workshop maps.