Here are the rules for starting trope pages on All The Tropes, as well as how to use the Trope Workshop.

Are you starting a work page instead? You can skip this entirely because Works are a Free Launch. (Unpublished works by you go in your own userpage namespace.) If you think you'll need help with the write-up, you can continue on this page.

New Trope Checklist

Look around to see if it already exists first. Looking at indices is a good way to help find trope pages.
Think up 3 examples of the trope. Statisticians need at least 3 data points to establish anything, and we do too.
Write a brief summary of the trope. Try to include related tropes in the description, which you should have found from step #
Take our write up and examples, and post it into Trope Workshop:, using any appropriate templates. (The shortcut for Trope Workshop is YKTTW:)
Let the proposed trope pick up responses for the next couple of weeks, and let people try to refine the description.
While you're waiting, look at other Trope Workshop entries, and let other people know if it's a good trope. Add any works using the trope you can think of. Let people do the same for your entry.
If other tropers have major issues, try to address them.
If enough tropers agree and enough time passes, go ahead and launch the trope by moving it into the main namespace. If you see Just Launch It Already a couple of times on any trope, feel free to move that one into the main namespace, too.
Add backlinks from the examples so people can find the new entry, and be sure to add to appropriate categories and indices.
Pat yourself on the back for a job well done.