The purpose of a search thread is to find a roleplay partner that you'll work well with and have fun with. Keeping these this in mind, here's a list of things you may wish to include in your search thread. You are by no means obligated to follow this guide to the letter, and indeed, including absolutely everything here may be overkill, but a good, thorough search thread can save you a lot of trouble.

Without further ado, here is a list of things you can add to your thread.

Your name
Your age (and what ages you are willing to RP with)
Your location/timezone
How often you are able to post
Your level of writing ability
The average length of your posts
How much roleplaying experience you have
How much research you are willing to put into an RP
A list of genres you like
A list of genres you don't like
A list of series/fandoms you want to RP
What format you prefer-- PMs, threads, IMs, e-mail?
What kind of characters you prefer to play (think about personality, gender, sexuality, archetypes, etc.)
Samples of your previous RP posts
RP plots for consideration
Post decoration, yes or no?
Profiles, yes or no?
An informative title (draw us in!)

This is not really an exhaustive list. Feel free to post suggestions so I can add them.