Macworld has a series of articles that I found helpful on maintaining your mac.

1. Essential Mac Maintenance: Get set up
   

   Perhaps the most important component to test is RAM…  Thankfully, it’s not difficult to do so, although a comprehensive test can take a while. Apple Hardware Test, included on the Mac OS X Install disc that comes with all recent Macs, has an Extended Testing option that tests your RAM.

2. Essential Mac Maintenance: Rev Up Your Routines
   
3. Five Maintenance Myths
   

   Myth #2: “You need to run the Unix maintenance scripts.”
   You may have heard about a collection of magical Unix maintenance scripts that OS X is supposed to run automatically. The story goes that because these scripts are scheduled to run in the middle of the night, putting your Mac to sleep or shutting it down prevents them from running—so you need to do so manually…

   An easy way to run the scripts manually is by using Mike Vande Ven Jr.’s free Maintidget 1.3, a Dashboard widget that shows you the last time each script was run and lets you manually run one or all with a single click. There are also innumerable tweaking utilities that provide similar functionality