1. Always give yourself a REAL EMOTIONAL DEADLINE.
Give yourself a deadline, but if you don't make that deadline REAL - meaning that there will be some sort of consequence that will make you FEEL bad if you don't make the deadline, you will never finish your script. (Examples: $1000 to your spouse or significant other if you don't make the deadline or simply book a theatre to put up your play before the script is finished!) Always make a real EMOTIONAL deadline so you have some leverage on yourself to really get the work done. A deadline without an EMOTIONAL consequence is an empty dream.
2. Write. Write. Write. And DON'T EDIT so much!
Get some actors to bring your script to life informally or in a workshop situation. Stop editing so much in the writing phase and edit in rehearsal when you can see and hear what is really working.
3. Take time off from writing and get into nature.
If you're in your room all day long on your computer or at Starbucks on your computer, eventually your creative juices may get sapped. A good strategy is to go outside into nature to refuel. Go to the park, go to the woods or go to the beach and just hang out. Shut down for a while. And you'll be amazed at the creative inspiration that will happen when you get back to writing, or even as you are just hanging out in nature doing nothing!
4. Write from your gut, your personal experience, and don't pull punches.
If your story is based on truth, change the names and write it. Writing about a real dramatic personal experience will power your play and your writing. Don't pull punches. Go for the KNOCK OUT. Dare to be painfully honest in your storytelling. That is great theatre!