Do it every day, more than once a day- maybe in bursts of like ten minutes at a time at first, just trying to do simple geometric shapes and letters of the alphabet, numbers, that stuff- another good one is drawing a random set of dots and joining them up (yes! join the dots IS good for you) because what you need to get down is hand-eye coordination on top of fine motor control. 

When you’re feeling sassy about it start doing some left handed drawing- anything, just doodling, but don’t expect it to be good! Just have fun with it. I ended up doing it as my warm up for drawing with my right hand, because even though it was my other hand it woke up my brain, and I think I drew much better after the challenge of just trying to get a curve to go in the right direction.

It’s really just a matter of perseverance- I’m not perfect at it yet, but I kind of like what each of my hands can do at this point. My left is more wild and whacky and good at backgrounds and layout, whereas my right is best for smooth lines and controlled volumes. Just keep trying! If someone as notoriously clumsy as me can get this far I’m certain that you can!