Gawd, can't believe I'm answering this question AGAIN:

Tip 1: search the forums for such words as "custom music" or "module making"

Tip 2: read up and learn about tracking. Good reading material is the Tracker's Handbook. Available from the United Trackers website.
Other sites to read up on are:
Modplug.com for not only the software but also hints and tips
OrangeJuice scenecenter
Pouet just for fun.