Shroud is one of my favorite streamers so I try and mimic his mouse settings as much as possible.

You want to start by actually lowering your sensitivity. As low as you can with it being playable is best. Personally, I play on 450 DPI and MS 3 in game. You also want to use raw mouse input, mouse acceleration is a no go.

Once you have you your settings in check then head over to

This will teach you aim tracking, strafe tracking and all sorts of stuff. I'd recommend using 3d aim trainer about 15 min before you play each day and you will notice your aim improve.

Also, this video has good tips.