- Backup Home Directory.
- Prune inactive users, old threads, etc.
- Check the mod / admin logs for suspicious activity and prune them.
- Run a repair / optimize on the database (easiest to turn off the board first).
I forget where I found these, but I keep a wiki with these and a few other monthly tasks listed.
I also do daily local backups of the db.
I have gzip on, why not?