a/c maintenance

What can be done for preventive maintenance for a/c systems?

In the past I have driven cars where the a/c never worked during my ownership. Now that I have two vehicles with functioning a/c I am paranoid I'm going to lose the a/c. What can be done to keep compressors from failing, leaks from springing etc.?

Also, what resources are out there to help with DIY a/c troubleshooting and repair? Or are these repairs best left to professionals or at least someone with the right tools?

In reply to twolittlebroncos:

Regular use is the best preventitive maintenance on an A/C system. This keeps the lubricating oil moving throughout the system.

Being that you really can't do any service on an A/C system without a machine to recover, vacuum, and charge the system. It should be left to the professionals.