Water heaters typically last 10-12 years. One DIY step you can take to extend the life expectancy is to drain the tank annually to rid it of collected sediment that causes corrosion. Most experts recommend draining once a year. I recommend draining your tank once and checking sediment buildup. Check it six months or a year later and compare the amount of build up to your previous amount. This will give you an idea on how often you need to drain your tank. If you have more sediment, you would want to drain more often. Less sediment, drain less often. Come up with a good schedule, that will keep your sediment build up to a minimum.
To drain the tank:
Turn off the power source to the water heater. You do not want it to heat while empty. This is very important. Failure to do so may cause damage to the water heater. To be on the safe side wait a few hours to allow the water to cool (running a hot shower will speed up this process).
Turn off the water supply to the tank.
Locate the drain valve at the bottom of the tank. Looks like a hose spigot.
Connect a hose to this and place the hose in a basement drain or sump.
If this is the first time you are draining, I recommend running the water through a strainer to judge sediment build up. If you already know your level, continue to the next step.
Open the drain valve at the bottom of the water heater.
Most experts recommend draining 3/4 of the water from the tank. If this is the first time, I recommend a complete flush.
Close valve and fill tank.
Once tank is full turn power source to tank back on.