Buy a Good brand, Trojan, LifeStyles, something people have heard of, not the truck stop bathroom generic ones.
Check the date. Condoms go bad.
Don’t use a condom you or your partner have been carrying in a wallet for the past year.
Put the condom on early. Pre-ejaculate can contain semen as well, and even with out penetration you can get pregnant from some heavy grinding.
Using a condom that comes pre-lubed with spermicide reduces the chances that you will tear the condom, or that your choice in lube might break down the condom.
Pulling out early shouldn’t increase your chance of pregnancy, but not changing a condom after ejaculation definitely can.
As to putting it on wrong. Remember to leave plenty of space at the end of the condom to hole ejaculate. Don’t by too big of a condom. This is the biggest problem people encounter with condom use. Very few guys are an extra large. but far too many men carry them. Get Regular in most instances. a regular size condom should accomodate 3-12 inches, measured from the base to the tip. Large will handle 6-14. and Extra large is sized for 9-16.
Only 5% of men could effectively use an Extralarge, but they accoung to 30% of Trojan sales. So either well hung men are having 6 times the sex, or a large percentage of men have purchased the wrong size, as regular will accomodate 85% of the population, and are too big for some men.
Myth of blowing in the condom to check for holes:
Blowing in the condom, does more harm than good. The condom will go on better “rolled on”. You want the tip to be air free, as air can cause the condom to come off during, or can force leakage around the sides. That and the size hole needed to be a problem is small enough that you would be unlikely to notice a leak unless you left the condom inflated for an hour or so to see that it was still inflated. That would ruin the mood in my view.