The idea is simple: spray cheap jewelry with clear spray paint to keep it looking fancy-cheap and not trash-heap-cheap. The spray should prevent tarnishing (see pics below for the sad tarnish truth) and keep inexpensive jewelry from staining your skin green/black.
THIS IS FOR YOUR CHEAPIES ONLY! Don't do this with any $$$$/heirloom jewelry, instead take it to a jeweler for professional restoration. Spray-painting fancy jewelry can reduce resale value and it does (full disclosure) kind of make jewelry feel sticky at first (although that faded quickly with time/wear)!
Check out my step-by-step pictures for details on the process and my results - which so far have been totally fine, but only time will tell if it truly worked. Other DIY-ers who love Forever21 as much as I do have had success with this method, so hopefully I will too! (And I will update this post if anything crummy happens later).
Alternative techniques to the spray paint method in this post: use clear nail polish, which seems a lot more time consuming, especially if you have as much bling as I do. Plus wiki says that's a no-no. Or get Tarn-X (which I know nothing about, but other people seem into).