Well... to find a good base shape, you have to work as small as possible. Personally, I start my sketches on an 1/1 inch screenspace, then I zoom on it to gradually refine the shape and add details.
I am reminded of a famous writer who tells of how he overcomes writer's block...he says " basically I sit in a room with 10,000 things and just pick one to write about. it doesn't have to be good writing, I just have to write about it. As for a modeler, it helps me to have an idea, but when i don't I just go through every…