For Windows:

Since Vista, the default installation automatically schedules regular defrags, although it doesn't hurt to take a look occasionally and see if its schedule fits your schedule, and that the scheduler didn't get turned off accidentally.

I would suggest running Disk Cleanup about once per week or so. Program settings can reduce the accumulation of trash, but some still creeps in and accumulates.

I generally try to run a Disk Check about once every month or two. It seldom finds anything to fix if the machine is okay, but can give you some warning if you need to do something when a drive shows first signs of a problem. The only onther common warning you may get is when you turn the machine on and nothing happens, and then it may be too late to do much.

John