Study television movie scripts. Many are for sale on-line. Pay particular attention to how specific screenplay terms are used. For example, V.O. means voice over. O.S. means off screen.
Read up on screenwriting format. The very appearance of a script can signal whether its author is an amateur or professional. Know the rules. For example, the preferred font for a television movie script is Courier 12 point. Many screenwriters use computer programs that format the script for them.
Decide on a genre. Some possible television movie genres are: family dramas, coming-of-age stories, bio-pics and true-crime. Think of a hook that will make your screenplay stand out.
Choose a story with strong emotional resonance. Make sure there's something at stake. For example, if the screenplay is about a woman confronting illness, it's much more powerful if she might die at the end. If the worst that could happen is that she'll have to take a day off from work, the audience won't care as much.
Make the protagonist strong and interesting, but give her flaws too. Think about characters you like watching. Brave as Indiana Jones was, he was afraid of snakes.
Use the active voice when writing. For example, "She walks into the room."
When you're done, type up the title page. Make sure to include your name and contact information.