If you're taking too much time to come up with the right words to fill up your blank page then you're probably thinking too much. And thinking too much (in front of the blank page) can destroy the fun and creativity of what spec screenplay writing should be all about.
You need to take risks and write where no wannabe screenwriter has gone before.
Everybody attempting to write a spec screenplay today is smart enough to figure out proper screenplay structure just by picking up a book by Syd Field or Mckee, reading a blog, or taking an online class. But 99% of these spec screenplays will lack enough original stuff inside of them. I'm talking about the cool ideas, memorable characters that actually seem real, and a fresh voice.
If you're a new screenwriter, don't forget how to have fun while writing your movie. Don't aspire to create a spec script that has been done before. You're better than that. Write something that you would want to pay $12 bucks to go watch.
Redundant, uninspired screenplays bore readers and get passes in coverage. Earn points for originality by being bold with your creativity.
Set yourself apart from the pack of wannabe writers by not following the latest trends you read about in the trades. Take risks with your characters and plot. If you've seen it before, don't write it again. Be different.
Here's a trick I use (besides writing super fast) that you might want to try in order to tap deeper into your own creative well.
Remember when you were a kid? You didn't think too much when you were a kid, did you? I know I didn't. I even ate paste some days. Anyway, because I didn't think too much, I had a lot more fun. I could create something fun to do without even having any toys around. How? Just by using my imagination.
It's all about imagination.
If you forgot how to use it, then I recommend paying attention to your kids, or other kids, playing in the park. Ask yourself: What are they doing that makes them so happy? How are they tapping into their creativity to amuse themselves?
NOW INSERT THAT BLANK SCREENPLAY PAGE
and go have some fun writing your screenplay without thinking too much. Write super fast. Make shit up and have your characters say and do some crazy ass things. Live a little. Don't worry about perfection, not yet, not while you're tapping into your creativity.
And when you have nothing else to say the words will eventually just...
I'm done writing out of my ass, for now. It's time to get cracking on another
Use your imagination. Be creative. Don't write something that we've all seen before.