Do not neglect:
Any irregularity, be it gas or water related. Call a competent plumber. This will most certainly avoid any unecessary dangerous situation.

In general you should know:
The location of your gas meter and the water mains stopcock. Make sure the isolating gas valve is clearly marked. If enclosed the key must be in a safe place and easily obtainable.

Checks to the stopcock ensures it does not seize. Simply turn on/off 3-4 times a year. Then open them fully and turn back a quarter turn. This avoids limescale around the valve.