Handmade jewelry is artwork and should be treated as such to ensure its longevity. Avoid wet and strenuous activity while wearing jewelry and always remove for swimming, showering, applying lotion, playing sports, sleeping, hand washing, etc.
If a piece gets dirty, clean with a soft toothbrush and a paste of baking soda and water, or warm soapy water. Avoid contact with stones. I use Dawn and an old toothbrush to clean my jewelry and it works very well. Also, a jewelry polishing cloth can be helpful if you are sure to avoid the stones and non metal components if applicable. I really like the Sunshine brand polishing cloths and use them on my own jewelry to bring back shine and brightness.
Sterling silver and other metals like brass, bronze and copper will change and patina over time. I use Renaissance Wax on most all of my work before it ships to you, which helps to revive and protect materials.
Store jewelry in a dry area. Avoid leaving jewelry in your bathroom or kitchen where there is moisture. I like to store my jewelry in a wooden box or jewelry box. When taken care of, handmade jewelry will last a lifetime and even become heirloom pieces.