Here's a great article on the maintenance steps you can do to extend the life of a hot water heaters.
"Do a Mini-Flush Performing a mini-flush on your water heater is easy.
Removal of sediments from the bottom of the tank is important to prevent rust, corrosion and improve efficiency. Although a full water heater tank draining and flush is best, performing a full flush is a bit of work and requires shutting down the water heater. This mini-flush works well, takes a fraction of the time and allows you to do it while the water heater is running:
- Place a bucket under the drain valve found near the bottom of the tank.
- Some drain valves have a handle. Others like the one in the photo shown here have a short handle-less stem with a slot for a flat blade screwdriver.
- Turn the valve counter-clockwise to release a few gallons of water into the bucket.
- Close the valve by turning it clockwise and drain the bucket."