Other diostories are a big help with how to do/what can be done. People like Violentfix, Justin and Luke are a great inspiration (reading Operation Rapier got me into making them). Movies and cartoons are a big help, as well as comics (big DC fan).
An unusual thing is music, if a song has a theme I really like or lyrics that I really get then I'll just go with it. My newest one is inspired by Judas Priest's "Out in the cold" (the title is also named after one of their other songs, Winter Retreat)
Other times I just get a figure and want to take some pictures "oh yes Cobra baby, take it off... wha?... I'm talking about his hood... you perverts!"