I just leave the processor performance on Automatic. I set the CPU to Never Sleep (allowing the monitor to go to sleep, of course) so that the Mac regularly runs the maintenance scripts. I make sure to repair permissions before and after installing new software. That's about it, really, for anything major.
Not sure if this makes any difference but, for OS upgrades, I prefer to download the file to my Mac, rather than have Software Update handle the install. Not sure why. Just makes me feel better, I guess.