It's an interesting topic, I think a lot of us have this problem. I always find it difficult to work on an effect. This is probably the most important phase in creating an effect. So it's logical that we hesitate to commit to an idea, I think.
While I'm so inspired at times, I don't have a problem with it, but it's pretty rare. What I find useful is surrounding myself with references of the things I want to create. The less sure I am, the more I am with an effect references that I collect.
The real problem is that we don't have a clear idea of what we want to do. One thing that helps me tremendously is checking out how other Vfx artists are handling the same problem as me when I need a stylized fire projectile screenshot the hell from the Inferno skin of League of Legends or Battlerite or any other game that does I like style and movement. And if nothing helps, I just force myself and start, ideas always come after a while.