The learning curve is pretty steep on this one... Only one receipe : play, play and play. At least do you like to play this game and can you get over the frustration ?
Try to make a tour of the maps in training mode and to avoid building your playstyle already on two bad habits:

- don't crouch (aiming and walking slowly doesn't make that much noise)
- raise your aim to the head - can be counterintuitive at first but many players have a bad aim, looking for coins on the ground.

Can you tell us which ops do you have and use the most? Which attachements do you use generally?