As much as everyone knows about metadata, most people still get it all wrong and significantly lower their chances of starting a lasting relationship.
Remember that your songs are leaving your computer and arriving to someone else's computer where they will be tagged and sorted into their own catalogs. Ownership (master and publishing) details are a must, but telling them the themes of your songs and even including lyrics can dramatically help your songs get found when the music supervisor is looking for something specific. Also always have your contact information in the actual metadata of the mp3.
Embedding album artwork or your business logo into your mp3 files also allows you to stand out.
Another important factor is to always send high quality mp3's ideally 256kbps or 320kbps.
- Mastered Instrumental edits of your songs are also very, very important and can be the difference between getting a sync and not getting a sync placement - especially with trailers. Send the instrumental edits in a separate folder.
- When presenting to ad agencies - it's a good idea to embed the cue into the metadata so you can pinpoint the exact area of the song that you feel fits their brand.