There are a few good measures to take when it comes to EDS.
1.) Better then touching the metal of the chassis, touch the metal of the Power Supply. The internal components of a PC as well as the PSU hold a fairly strong charge for up to an hour or so. By toughing the metal of the power supply, you will evenly ground yourself to the electrostatic charge of the PSU. Don't worry, if it's off and unplugged you won't get ZAPPED... Do this everytime you walk away and come back to the PC.
2.) Antistatic Wriststraps are a very cheap and effective way to keep you grounded to the chassis while doing prolonged work inside of it. Kind of a pain though clipping and on clipping it from your wrist... And the springy wire is a pain sometimes too.
3.) Ultra-Products sells an excellent (Anti-static) work mat. They have a few sizes to choose from. I've got 1 of the largest size and one of the smallest size. The larger one I use for a work surface for cases and the smaller one I use for working on MOBO's, GFX Cards, CPU's ETC...
4.) Also, don't wear just socks and shuffle your feet around the house on carpets... BAD IDEA!!!
5.) Invest in a few (Anti-static) Bags for safe storage of components you aren't using but would like to save.
6.) Electro-Static Discharge is most likely to happen with (COOL / DRY) air.