According to David Trottier’s The Screenwriter’s Bible.

If you write a script that features a character that has a clear and specific goal, and there is strong opposition to that goal, leading to a crisis and an emotionally-satisfying ending, your script will automatically find itself in the upper 5%.

—David Trottier, The Screenwriter’s Bible

1. Don’t include fancy covers, artwork, illustrations, or storyboards.
2. Don’t number the scenes. This is done after the script is sold.
3. Don’t use fancy fonts or proportional-pitch fonts, only 12-point Courier or Courier New. (Note: This website uses neither of these fonts, so do not use it as an example.)
4. Don’t justify right margins. Leave the right margin ragged.
5. Don’t bold or italicize.
6. Don’t use camera and editing directions unless necessary to move the story forward.
7. Don’t date your script in any way. Scripts get old fast.
8. Don’t write “First Draft,” “Final Draft,” or any draft.
9. Don’t include a suggested cast list or character list with bios.
10. Don’t include a list of characters or sets.
11. Don’t include a synopsis — you are selling your ability to write.
12. Don’t include a budget.
13. Don’t include a header (such as your name or title) at the top of each page.
14. Don’t ignore errors in spelling, grammar, and punctuation.
15. Don’t “cheat” by using thinner left and right margins, by squeezing extra lines onto a page, by using a smaller typeface, or by widening dialogue lines beyond the standard 3.5 to 4 inches.
16. Don’t type CONTINUED at the top or bottom of each page.
17. Don’t send out a script that is over 30 pages.*
    
    *In The Screenwriter’s Bible, David Trottier says, “Don’t send out a script that is over 120 pages”; however, the HAUS Film Festival Screenplay Competition requires screenplays to be no longer than 30 pages.

The Screenwriter’s Bible is an excellent resource

All screenwriters should be familiar with this excellent book.