The following tips apply to Snow Leopard but may also be useful for other versions as well. All are based on recent good and bad experience.
- Remove Intego Antivirus. I had this for a number of years and only recently found that it was causing the computer to crash and hang on login or logout. I would rather have kept it but since removing it I have had no problems. I am in general in favour of having an Antivirus and if you must have one, place Clam XAV (which is free) on your computer but do not install this to run in the background, only when you click on the programme icon. Otherwise again it will slow everything down.
- Remove CleanMyMac I used this until last year, I ran it perhaps twice. The result was that I had to reinstall the machine on one occasion. In general a nice idea but not perfect.
- Ensure you have at least 15% of your drive space free, if you fall under this your Mac will start to slow down to a near death experience. If your Mac has less than 15% free its time to delete files or perhaps buy a second HD. Second USB based drives are ok, although not fast. If you go for the USB option only place files which your computer is not constantly accessing. Movies,music, pictures, word processor files are good examples.
- Install SecondBar. Snow Leopard does officially support two displays, but only one menu bar. The result is some confusion while using second display. This handy free app will install a menu bar on the second display, thus improving usability. It’s free, and does what it says although is not perfect.
- Check your menu bar, are you running apps you no-longer need? If so remove them as this will also slow things down and some poorly made apps may even increase stability problems.
After nearly buying a new computer I tried all of the above tips and my six year old iMac now works like a charm! Thus saving me a nice pile of cash.
I hope these five simple tips help. If you want more info here are some links, I will not give you the links to the software you should remove as well you should not be installing them anyway:)