It is hard to sit down and start, so I usually trick myself with: 'I will just draw one line today and the rest can follow tomorrow'. Once you get going is always more than one line (I'm an amateur Blender user, so 2 lines are already a polygon). This stuck with me (volume, not 'quality');
https://www.blenderguru.com/articles/7-habits-highly-effecti...
p.s. And after N lines * N completed pictures you will automagically know what you want. In my case certain image will form (or an idea) - this could take days/weeks, this are usually small and stupid, but that doesn't prevent me from realization (or at least an attempt) - it's all just for /me.
