The first part of this tutorial is how I get over my art block.
I just doodle and try different things until I get something. Don't try to be perfect just get a flow/rhythm started.
Sometimes it may be that you're just too busy/stressed to draw, and can't relax enough to do it. However, once you just start going into it then it come naturally to you, or wait when things calm down. (This has been me for a while.)