Plan
Like most things, planning ahead and getting an early start is key. It gives you the time you need to select the perfect ring. You may have a basic idea of what you want, but that doesn't mean you won't find several different bands you really like once you start shopping. Give yourselves at least two months to browse, research, price, and revisit the rings that catch your eye.
Personality
Just because you and your fiancé are a perfect match doesn't mean your rings need to be. Feel free to pick wedding bands that reflect each of your style sensibilities and tastes. Some aspect should match, which can be as simple as metal or inscriptions.
Remember, your ring should respect your lifestyle: Those who enjoy sports or music should opt for a slimmer ring with rounded edges (appropriately called a "comfort fit"), rather than a wide, bulky band. Those who work with their hands will want a simple, solid metal ring, as stones can come loose and carvings will trap dirt. And those who are highly allergic to certain metal alloys will want to invest in platinum, as its purity renders it hypoallergenic for most people.
Proof
Take the time to make sure you are buying a reputable ring. Wedding bands should have two marks inside the band: the first is the manufacturer's trademark (which proves that the company stands behind its work), and second is the quality mark (24K or PLAT, for example, which proves that it's what they say it is). If the ring consists of two or more metals, make sure there is a quality mark for each. Ask your jeweler to point out the designer name and metal type.
Perpetual
Pick a ring that's going to look great for a long time. So, select a style that will look as great with jeans on weekends as it will with a business suit or evening dress. Stick with a basic shape and a clean finish, and avoid unusual stones that will be over next week. Mix metals -- like many ring designers are doing -- if you're someone who wears both gold and silver on a day-to-day basis. Make sure your wedding band is one you'll want to wear everyday.
Perfect Fit
Never finalize your ring size in the morning (you retain water from the night before), after exercise (fingers swell), or when you're extremely hot or cold. Do your "final fitting" when you are calm and your body temperature is normal.