Hi, those before me have given good advice, but it might be worth adding the following;
a) if you use an anti-oxide cleaning liquid or cream, you need to thoroughly wash and dry the residue off, otherwise it will be the residue or dampness which would turn the silver black again even more quickly than before
b) some skins are more acidic than others, and can speed up the build up of the oxides on silver. The recent heat-wave wouldn't help (heat and damp conditions are not good for silver)
c) when storing and not wearing silver, keep in a cool dry place...silver will still oxidise if not used at all but this will help, and you can also buy anti-acid tissue and felt for bigger items
Hope that helps, and it does polish beautifully!