Weight is everything
Two 14K rings that look alike can differ in value by half, because width and thickness change the weight. A comfort-fit band is heavier than a flat band of the same width.
Weigh your ring in grams for the real number. A kitchen scale that shows 0.1 g is enough.
Stones and settings
A diamond or gemstone adds weight but not gold. Buyers who pay for gold will remove or deduct it. Small diamonds rarely add much resale value; larger ones are worth selling separately.
Brand-name rings (Tiffany, Cartier) can be worth more than gold. Check inside the band for a signature.