Here’s a quick tip to really help you achieve a nice looking digital painting, no matter what it is: flip your canvas horizontally!
Flipping it horizontally will show you most of the composition problems you have in your painting, even if you don’t realize they are there. When sitting and working a longer time, your eyes will get used to the painting, and consequently get used to any errors the painting may have in a composition sense. Even sitting only a few minutes with a painting may ease your eyes to these problems.
As you flip your canvas, your brain doesn’t know what’s happening – suddenly there’s a new painting in front of it! You will immediately see that the painting might be very heavily directional in a certain way and lack balance, so you can continue painting on it while it’s flipped until you get a good balance back, and then you flip it again.
Flipping back and forth like this will solve a ton of compositional problems, and it will help you spot them much easier.
Go to your key commands in Photoshop (if you’re painting in it, which I highly recommend), find “Flip Canvas Horizontal” under Application Menus – Image and set it to a key command (I use cmd-H on Mac and ctrl-H on PC).