You can drain water into a bucket or you can connect a garden hose to the valve to drain the water to a sink or to the outside. When you are ready to drain the water, place the bucket beneath the valve or place the hose into a sink. Remember, the water will be very hot, so be careful. Turn the valve counter-clockwise to open it. A couple gallons should be adequate to remove the sediment build-up, you can judge by the clarity of the water. Initially, it will be dark or rust colored and then will lighten as the sediment is drained out.
When you are done turn the valve clockwise to stop the water. Wipe away any water with a rag and recheck the valve in a minute or two for any leakage. Tigthen the valve closed with a wrench if necessary. In our experience the valve can be difficult to close completely and so water will continue to drip from it. For that reason we recommend that you have slip-joint pliers or a similar tool at hand to turn the valve completely off. However, be careful not to overtighten or you may damage the valve, especially plastic models.
If you turned off the water supply, circuit breaker or set the gas valve to "Pilot", restore them back to their normal positions now.