Your computer is just like your car and yourself.  A little bit of preventative maintenance goes a long way!  First and foremost is you must have a capable anti-virus program on your computer.  You will also need a anti spyware program that will detect the spyware that is trying to install itself.

You should setup up a regular schedule for your computers maintenance.  Don't try to do every task on the same day.  If you break it down over a month, you will be able to keep up the regular maintenance without taking up too much time.