Cache - Google Speed Test

I'm just discovering Google Speed Test; for those that don't know what it is, it's an extension for Fireworks/Firebug. It runs a test and displays the top "offenders."

I've spent a little time using the Google Speed Timer extension for Firebug. You open up Firebug inside Firefox and select the speed test and it lists the top problems with you sites as it relates to speed.

The number one issue for me is site caching and I'm wondering how I could fix this.

I have a database driven site abd I'm wondering if anyone has any ideas? What I should start with?

Are there some quick and simlple things I can do?

Ideally, I'd like to cache a lot of my images but once changed, I'd want to make sure they were re-cached.

I've looked all over for how to do this and I can't seem to find a clear solution.

Does anyone here have some good solutions? Ideas?