Did you know Engagements have a season? Most proposals occur during the holiday season: between Thanksgiving and Valentine's. If you are thinking of popping the question--or hoping someone will propose to you--it's a good time of year to learn about rings.
Cut - Which shape is the most flattering on her hand? If you are buying a set that includes her wedding band, too, what shapes will nest into or next to the wedding band. Cut also considers the quality of the cut by the jeweler who cut the stone; a well-cut stone will radiate more light.
Color - In diamonds, this is how "white" or clear the stone is instead of one that is yellow-ish. Other stones should have respectively accurate color, too.
Clarity - Is the stone "crystal" clear or "foggy"?
Carat - How much does the stone weigh? This translates fairly well to the physical size of the stone, too.
Is she a traditional diamond girl? Does one of the stones need to reflect a special time like a birthstone? Will an emerald speak to her Irish heritage? Will she be touched by a ring that is humane and eco-friendly; or will she be disappointed if it's not a diamond?
Gold? White gold? Platinum? Which color of metal does she wear the most? Or, has she expressed hope for a very traditional look?
A local jeweler can spend more personal time and attention on your ring. They can also work more specifically into your needs and budget. A creative jeweler can take all your ideas and personal touches and get you the most ring for your money. You'll also get a ring that is unique to her instead of one that looks like all the others her friends are wearing.
The diamond industry has spent a lot of time and money trying to convince men to spend two month's salary worth of money on the engagement ring. That may or may not be realistic for you both. Would she rather wait for a fancier ring (and forgo travel or other luxuries while saving up); or, would she rather have a ring sooner and start wedding planning?
If you look at money you have already saved up, set a budget and shop within that. You might also even fib about the high end of your range when shopping....it's their job to get you to buy the nicest ring you can afford.
If you are not certain about the answers, take her window shopping. A romantic walk around The Domain will give you the chance to see which sparkles catch her eye the most. Be sure to wander through the Outrageous Gallery where you can pretend to be shopping for a high-end kaleidoscope.
Or, check with her most trustworthy friend. Chances are, the girls have all talked about their "dream ring" and they can help steer you in the right direction.