Wearing a watch with combined metals is a simple and practical way to tie your jewelry together.
Layering necklaces and bracelets makes it easy to wear gold, silver, and other metals at once.
If you wear a platinum wedding band, for example, select your other jewelry as if the ring weren't there. Hardware like zippers can also (usually) be ignored.
Avoid wearing five silver pieces with just one gold piece, or vice versa. Instead, try to find balance with the number (and size) of your pieces.
Like the rest of your outfit, your jewelry doesn't have to "match" but it helps to find a flow in the style (ie. casual vs. formal).