Shower.It's not a great idea to shower with your jewelry on, but once in a while isn't going to do any lasting damage. Just make sure to dry it after.
Swimming Pool.Take your silver off. Chlorine is a pretty harsh chemical, so if you accidentally forget to remove your silver jewelry before hopping in, make sure to rinse and clean it afterward.
Hot Tub. Same idea as the swimming pool, but there's even more chlorine in the hot tub and the heat can accelerate the chemical reaction.
Hot Springs. The sulfur in natural hot springs will wreak havoc on your silver. Unless you're going for that "dark oxidised" look, avoid at all costs.
Bonus Tip: Chemicals in lotions and perfumes can also cause your jewelry to tarnish. Apply them first, let them dry, and then put your jewelry on. This alone can make a HUGE difference in your silver's luster.