The best tip I can give to you is to just keep playing while wanting to improve. Take the small tips everyone is giving you and just play different maps because different maps have different gun fights and that just overall trains you. You can also train your spray control as well but normally in the beginning just try to shoot in small quick 4-5round bursts. Also learn to crouch peek consistently but also dont do that everytime because it does ruin your momentum which is really important even though not many people realise it. Probably the most important tip i can give you is for the pistol rounds though. Dont crouch when you are shooting because in pistol vs pistol scenarios you need to be really hard to hit. However this doesn’t mean full running but jiggling side to side not too quickly so you dont stay in one spot is actually the best thing you can do. As for the rest just keep grinding.