Condoms can provide important protection against sexually transmitted infections (STIs) and unwanted pregnancy. But believe it or not, many men make user errors that render them less effective. in fact, this happens up to 30 percent of the time according to the American Sexual Health Association. The blunders range from using an expired condom to accidentally wearing one inside-out.

Amber Madison, a psychotherapist at the New York Institute for Psychological Change, sex columnist for Men’s Fitness and author of “Talking Sex with Your Kids,” offers these tips for avoiding potentially costly bungles.

Gear up at the starting gate. National Institutes of Health (NIH) studies found 43 percent of college men and 51 percent of college women used a condom only after starting intercourse. Also, 15 percent of the men removed the condom before finishing. Since men leak seminal fluid from their penises both before and after ejaculation, both of these moves are bad ones, according to Planned Parenthood.

Use it, then lose it. Use a condom only once. Even if you're on a roll between the sheets, don a new one with each erection, Planned Parenthood recommends.

Stay current. “Expired condoms are much more likely to break,” says Madison. Lubricated condoms without spermicide are typically good for about five years after they’re manufactured. With spermicide, they’ll last for about two years. You can find the expiration date on the box, as well as on the wrapper itself, usually near the perforation.

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Open with care. Open the wrapper carefully with your hands — not your teeth. “You can actually rip the condom along with the wrapper,” says Madison. The American Sexual Health Association says 10 percent of condom users make the mistake of opening the package with a sharp object.

Never flip-flop. After you unroll the condom, take care not to put it on inside-out. If you do, stop right there. “You’ll actually want to grab a new one,” says Madison, “since the outside of the first condom has potentially touched seminal fluid.” The NIH study found that 30 percent of college men put the condom on inside-out.

Add some lube. Most condoms come pre-lubricated, but adding a few additional drops of water-based or silicone lubricant will help prevent the condom from breaking and slipping. Never use an oil- or mineral-based lubricant with condoms. They can disintegrate the latex and cause it to tear.

Remember that size matters. “Many men don’t understand the importance of proper condom fit,” says Madison. If the condom is too large it could slip off during sex. Try different brands and sizes until you find one that works. Madison recommends finding one that’s snug but not too tight, with enough room at the tip for ejaculation (Planned Parenthood suggests a half-inch). In the NIH study, 40 percent of college men and 46 percent of college women did not leave any space at the tip.

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Make a safe exit. Remove the condom as carefully as you put it on. After sex, hold the condom against the bottom of the penis while you pull out. Unroll the condom slowly, and hold it away from the body to avoid potentially spilling semen. Wrap the used condom in a tissue and place it in a trash can (never flush condoms, which can damage sewer and septic systems).

Keep condoms out of your wallet. Having a condom when you need one is key. “The biggest mistake anyone makes with condoms is not using one when they intended to,” says Madison. But don’t carry condoms in a wallet or makeup case, or you run the risk overheating them or puncturing them with a sharp object.

Karyn Polewaczyk is a Boston-based lifestyle writer and creative strategist.