1. Keep it clear
As cluttered as the garage might be, its a good idea to keep items away from your water heater.
2. TURN THE WATER OFF!
This water is HOT! You don't want to be tinkering with the water heater and accidentally give yourself 2nd degree burns. Make sure you turn the water off before you start fixing the water heater!
The first solution to any problem is identifying it! To do this, you should make sure you know what kind of water heater you have. There are natural gas, electric or propane, tank-type, and tankless-types.
Debris and sediments can build up in your water heater, which causes them not to work as well over time. Once a year its a good idea to drain your water heater.