I'm having trouble starting out with my potential screen play. I mean, I know I need to write it, but the words just aren't forming on the page right now, and it's getting kinda frustrating.

I seem to be good at writing the intro. sequence (the first few pages), as well as the ending sequence of screen plays. Everything in between just sorta fizzles out. I need to be able to flesh out the middle portion of the plot of my screen plays, so I'm asking for ideas and tips from you guys?