just make sure you have enough disk space for the rebuild of your database to complete correctly. always make a backup before touching your database in this way. close your forums before you do it. dont forget to reopen your forums afterwards.
overall, running the optimization is quite simple. you can find a lot of information on what the procedure does by searching google for "mysql overhead" and "phpmyadmin optimize tables" -- most of those Google results should be very human-readable, and not require a large technical vocabulary to understand.
