Hello,
Being
wait-listed, although frustrating, is a sign of sincere and significant interest in your candidacy.
First, review your note from the adcom advising of your wait-list status for any instructions or guidance on what to do or not to do. Most important, follow that advice! If it does not advise against sending additional information, you could write an update letter discussing any relevant development since the application and reiterating your interest in the program. You might also have an additional recommendation sent. Finally, if they offer feedback on the application, obtain it, though most programs don't offer such input.
Best regards,
Cindy Tokumitsu
Senior Editor,
www.Accepted.com