Ideas for Screenplay

I thought I have plenty of ideas to write a screenplay with but when I sit down and try to decide on what to write, I hesitate to choose any of them.  I do not know why.  Maybe I have fear in disclosing my ideas or try too hard to be "perfect" on my first story.  Joe Vitale says that you should try to do something you are afraid of most.  What would it be in my case...?