Restart your mac once a day. This will reduce memory fragmentation from the opening and closing of programs. Make sure you login to Empower before leaving for the night if you restart at the end of the day.
Rebuild the desktop once a month. At startup hold down option & open apple keys. The desktop files keeps track of where your files exist on the hard drive. Rebuilding the file delete obsolete information which would slow down your mac.
Run Disk First Aid if you suspect a disk problem. Quit all applications. Go into your hard drive - applications folder & double click Disk First Aid. Highlight your hard drive + click repair.
Clean your mouse every 3 months. Turn off the computer. Flip the mouse over so you can see the ball. Use 1 hand to hold the outside part of the mouse while you use your fingers to turn the indented part next to the ball. The bottom plate should come off. Wash the ball with soapy water and dry thoroughly. Use an eraser to clean the hardened dust off the rollers and shake into the trash.
Avoid opening and closing programs. Every time you open and close a program a small amount of memory is lost to fragmentation/memory leakage. It's better to leave programs open if you might use them later in the day. You can check how much free memory you have by going to the apple menu - about this computer.
Keep your files in the documents folder not the desktop. Only your documents folder is backed up and files on the desktop are easily corrupted.