All sterling silver tarnishes through a process called oxidization. This can not be prevented but can easily be cleaned with things such as treated polishing cloths or with the homemade cleaning methods below.
I do not recommend silver dips for removing oxidation from your silver jewelry. Many will leave microscopic pits in the silver causing it to darken faster. I do recommend preventive care by storing your jewelry in a closed box or plastic bag. Silver will tarnish when left out exposed to air. Storing in a small air tight container will help prevent some tarnishing. Please store your jewelry in a dry place away from makeup and chemicals.
Silver reacts with chloride so it is best not wear it in a shower or swimming pool.
It will not fall apart while you do, but it can be damaging if it is done repeatedly over time. To remove dirt and oil from your jewelry you can wash the piece in warm water gently using a very soft cloth and a little bit of mild soap such as ivory flakes.
Dry with a soft cloth.
PROFESSIONAL TARNISH REMOVER:
"You can also use a professional tarnish remover made for jewelry. Be sure it is safe for your metal, pearls, or soft stones like opal or turquoise (if you have that kind of jewelry). Most of these pastes can be applied then removed with a dry cloth. If the piece is antiqued you want to be careful not to remove it.
If you prefer a cleaning cloth, a cloth called Sunshine Polishing Cloth is very popular. The cloth will turn dark but can still be used for a very long time. The cloth contains chemical cleaners that will give a lasting luster to your jewelry. You can use it when you notice that your jewelry starts to appear dull. I do not recommend any other brand of polishing cloths because some of them are not safe on stones. You may want to be careful cleaning a piece that has intentional oxidation because the cloth will remove it as well. Again as with any cloth and or cleaner be very careful with pearls. I do not recommend the use of any polishing cloth on pearls.