The life of the water heater might be increased or extended by periodically flushing the water heater. The theory is that sediments can collect in the bottom of the tank contributing to tank failure. In order to drain water from the the water heater (just a few gallons, NOT the whole thing) you must utilize the valve at the bottom of the tank (has the same spout threads as your garden hose). If you have a brass drain valve, your water heater is of the best quality and you might flush it out once a year.
Unfortunately, a plastic water heater drain valve is the cheapest and most likely to cause problems if used. If the drain valve does not close fully, you have just created a need for a replacement drain. The next problem that can occur with a cheap plastic drain valve is that it often breaks off as one attempts to unscrew it for replacement. This makes the replacement more time consuming (read: understatement). If you have a plastic valve I would recommend not using it except for an emergency.
If a water heater is in a room that you rarely go into OR has no floor drain close by, it can be a good practice to have a water alarm near the device. If the water heater starts to leak you’ll know immediately. If/when you discover that your water heater is leaking and it is a small leak, don’t panic. It is rare for a water heater to suddenly increase the amount of water that is leaking, but it is best to call me immediately if ANY water is coming out.