First, I would check out /var/log and see what older logs you might be able to delete...they can really add up faster than you'd think. I would then set up a cron job (weekly or so) to remove the older ones regularly. Also, take a look arounfdat config files you edited or whatever. Some editors, joe and pico in particular, will create a backup file with the same name, but ending with the ~ character. Those can safely be deleted as well, and the configs for the editors can be set not to create those backup files. Also, check /tmp for unneeded files.