Before draining it, make sure the propane and/or electric is turned off.
#1, if you have an atwood water heater, there is not normally an anode rod in it, so remove the plastic plug
#2 if you have a suburban water heater, at least once a yr, pull out the anode rod and see if it is 90% gone, if so get a new one and while it is out.
IMPORTANT:
Be sure water has cooled off before opening the water heater drain, no need to get burned by hot water, turn off water heater and run water out of a faucet till coolish.
Turn off city water/water pump and run faucet until pressure is all relieved, trust me on this one, don’t ask how I know but the water drain plug come sout like a bullet if system is still pressurized and water goes spraying EVERYWHERE.