GEMSTONES ARE ALL ABOUT COLOR.
Unlike diamonds, a gemstone’s primary characteristic (and source of value) is its hue and saturation. Take time to research different varieties of your gemstone and decide which coloring you enjoy best then make this a priority once you begin to shop.
BUYING A GEM IS NOT LIKE BUYING A DIAMOND.
Diamonds are very strictly graded and sorted by standardized criteria, but the same is not necessarily true of gemstones. You won't be able to find, for example, a "VS1" sapphire--in fact, even top quality color gemstones are simply graded as "eyeclean" or "loupe clean". Shopping for a gemstone is much more visual: take the time to view many samples side by side to decide which you enjoy best.
PRICING IS NOT LINEAR.
Certain factors create exponential increases (or decreases) in price because of relative rarity: namely color, carat weight, and clarity. So a large eyeclean emerald will cost much, much more than a comparably sized included emerald simply because there are far fewer of them to go around.
DON'T BE AFRAID OF TREATMENTS.
A gemstone that has been treated or enhanced does not mean it is of poor quality or that is not a genuine stone. In fact, certain treatments are standard procedures for many gemstones. Heat treatment is used nearly universally for gems such as ruby, sapphire, tanzanite, citrine and amethyst, while nearly all emeralds on the market are oiled or wax/resin filled to improve clarity. It is certainly possible to find stones that are not treated with these techniques, however, they typically command much higher prices.