Look for the official seal. Products approved by the U.S. Pharmacopeia Dietary Supplement Verification Program (USP-DSVP) meet certain safety and quality standards.
Check how much you're getting. For trace minerals such as iron, fluoride, and zinc, it's safest not to exceed the daily value. Don't forget that what you get from fortified foods, like many breakfast cereals, counts, too.
Choose a product for women. It's more likely to contain the right doses of the nutrients you need most -- calcium and vitamin D for better bone health, folic acid to prevent birth defects, and iron for replacing what's lost during periods. (If you're pregnant, take a prenatal vitamin; it has more of what you and your baby need.)
Ignore gimmicks. Whether a vitamin is derived from natural sources or synthesized in a lab, your body uses it the same way. There's also no need to pay more for allergen-free multis if you're not sensitive to specific ingredients.
Beware of dangerous interactions. Pay attention to the warnings on labels, and always tell your doctor or pharmacist what supplements you're taking.