You are lucky to live in a place where the utility company doesn't turn off your water on a schedule because there is a water shortage. Those of us who are used to it know that nothing particularily bad happens.
If you plan to work on hot water part, turn off your water heater no matter if it is powered by electricity, gas, coal or uranium rods (sun-powered are a separate case, refer to their manual). Drain any hot water from it beforehand. You don't want hot water leaking on your hands in some confined space where you cannot readily run away, do you? It probably has a valve that won't let the hot water into the cold side, but one could never know how this valve feels like, so it is better not to have hot water available to burn your hands it even if you don't plan working on the hot side.
Washing machines, dish-washing machines, water coolers, coffee machines, etc, ... anything connected to both water and electricity must be turned off and unplugged from the mains if applicable. Forgetting one or two of these is less important, they don't have the water heater potential for doing unpleasant things.
When turning off any rarely-used water valves, esp. old rusty ones, be prepared that (1) they may not close absolutely tight (you may get a small amount of water flowing from open pipes for the whole duration of the repair) and (2) they may start leaking from the shaft. The shaft leak usually, but not always, stops later by itself.
Ok, you turned off the water, did some repairs, now turn it back on.
Check for leaks.
Run water from all taps until it stops coughing air. Look for any signs of mud or rust in the water that comes out first. If there is any sign of mud or rust (it depends on the type of plumbing and the quality of your local utility water), you may need to run the washing machine on the shortest program without any clothes in. You don't want your clothes washed with rusty water, beleive me.
Check for leaks again, everywhere, even where you didn't touch. One can never be sure.
Turn back on anything you turned off.