InmanNews.com ran a good little snippet on this morning's news bulletin about draining your water heater. Since I don't want to just re-post their article here (pesky copyright laws!) I did a couple Google searches. Links below. Draining your water heater from time to time will increase the life of the heater, and ensure you have more hot water for your daily needs.
DIY Network - Drain Your Water Heater - seems like a fairly thorough article; great pictures of each step
The Natural Handyman - chatty & entertaining, but don't make this the only article you read before atttempting at home
Lowes - fairly short but with excellent illustrations
HGTV - amusing pics of having a professional plumber do the job. Being a total girl, this is the option I choose. I don't do home maintenance; I exercise my check writing skills.