There are TONS of videos on YouTube with great drills and guides on how to become a better player. Many of them don't even require you to shoot paint, here's a few examples
First things first you needs to make sure your marker is setup right. Having a comfortable and consistent shooting platform is one of the fundamentals, if this is all out of whack then don't expect to be able to hit the broadside of a barn when under pressure,
Here's a nice vid:
For me, one of the most important things in paintball, both sup'air and woods is getting as comfortable with shooting out both sides of your bunker. Holding your marker and shooting with your off hand should feel just as naturalas with your dominant hand. One way I trained this was simply carrying my marker around the house with my left hand, get comfortable with it. Spend ages locking into a 'gun up' pose (as in ollie's vid above) with your off-hand, next time you play FORCE yourself to prioritise your off-hand, this is not something that happens overnight but will come with time
One basic skill you can start to practice without using any paint is snap shooting. Here's a nice vid that intrcudes how you can use a mirror to help yourself be aware of how much you are exposing when breaking cover
EDIT:
Here's a couple of the Dynasty training vids, a bit dated, somewhat cheesy but there's a lot of good stuff
Vol 1
Vol 2