My problem usually isn't a lack of ideas - in fact, I tend to have far too many of them. My problem is that I can't complete building in time.
What I had done the last years to avoid that, was the following: I wrote all my ideas as List, for example I want build a palace, want to build flying Islands, use a Color Puzzle, implement Cutscene xyz and and and. To every point I gave a Weight from 1 to 10. Where ten is the most important one. Then I began with the building and start first of all with the ten Points. After I finish I went to the nine Points and so on. The last Btbs where I finish a Level I receive everytime to five or four. Of course, this was never the completed List of ideas in the finished level, but this is for finishing in time a already a good Level. So I can avoid to dissipate my time and energy with no so important points.