I'm torn between a few things...
One is storyboarding - I struggle to find the motivation sometimes. It's just that I can either burn out page after page of composition ideas or I draw a blank. I have to do it in bursts.
Another one is background. I do find it somewhat tricky, but that's not the only problem. The problem is working out how much to show in each panel. In action scenes you're not meant to show a lot of background so that attention isn't drawn from the action, but there's an amount of indication you have to make. That balance is a bit of a hassle.
Finally just finding the motivation and time - I've got to balance it with my full time commitments as well as my other creative projects and it's a bit crazy sometimes.