Things to Look For:
Look for a gold mark (12K, 14K, 18K), sterling silver mark (925) or platinum mark (950, 999).
Look for a maker's mark (small initials, signature or symbol).
Evaluate the overall condition of your piece. Is it smooth with little indication of wear or are there dents/scratches?
If your piece contains gemstones, check the condition of the stones. Look for any missing stones and gemstones that are chipped or cracked, as these will detract from the overall value. Stones in excellent condition will photograph and sell much better.
Does your piece have an appraisal? Jewelry rarely sells for an insurance appraisal price, but buyers will pay more for a piece that has appraisal paperwork. So it's worth tracking down those papers!
Does your jewelry have a story of cultural or historical significance -- for example, did it once belong to a celebrity or historical figure? A good story can add to the value of your piece, especially if it's documented!