Q: Troubleshooting/fixing slow performance?

I gotta 2008 iMac with a 2.66 GHz Intel Core 2 Duo / 2 GB 800 MHz DDR2 SDRAM running 10.9.1 and this thing runs slow as mud. When I have my usual suite of apps open for work (Chrome, Outlook, Word, Messages, sometimes iTunes or Spotify) everything basically grinds to a halt--it can take up to a minute to respond to a mouse click, and often text takes twice as long to appear as it takes me to type.

I have basically the same computer at my office at work (I think), and I don't have nearly as many problems.

Differences: I have four user profiles on this computer and only two on my work computer. I also have more stuff stored on this computer.

What do I need to do to troubleshoot/fix this?