OSX defragments automatically, so no worries there. As a regular procedure, I would at a minimum add logging out or better yet rebooting every few weeks. This clears the virtual memory cache files that tend to build up and slow things down. I'm also a huge fan of
AppleJack, a maintenance tool run from single user mode. It automatically checks the disk for any errors, repairs permissions, clears caches, looks for corrupted preference files and does those Unix cron jobs that won't get done unless you leave your Mac running 24/7.