✖ Manually defragment your Mac’s hard drive. There’s no point. It doesn’t make any difference in modern OS versions.
✖ Allow your hard drive or flash storage to fill up to the point where it’s more than 90% full.
✖ Worry about cron jobs or other Unix maintenance routines. OS X takes care of the housekeeping.
✖ Leave your user account logged in if you use a shared computer at work. Always log out before walking away.