Are there rules, customs, suggestions, expectations, or other guidelines?
Should a Filk song use some of the lyrics of the original tune, or should one strive to write totally original lyrics?
Other?
For those as lost as I was: Wikipedia on Filk
Filk.com has a lot of information, but I can tell you a few things - not all filk is lyrics sung to a familar melody; some filkers write their own melodies. Original lyrics are good, but if you can make some of the original words have a completely different meaning, that’s really good. For example, a filk of “Norwegian Wood” about sentient swords in D&D ends with "Now I use a club - isn’t it good, no-ego-wood.