Abstinence (no sexual touching or intercourse) is, of course, 100% effective against the transmission of hiv, std's (sexually transmitted diseases), and pregnancy. Sexually active individuals should know the hiv status of their partner and themselves (positive or negative by getting tested), use protection (latex condoms or polyurethane condoms are the only effective types against hiv-lambskin condoms allow hiv to penetrate through the condom), and long term relationships.
Condoms must be used correctly. A condom package is only meant to keep the condom lubricated. It cannot withstand heat or cold. Always check the expiration date and feel the package to make sure that the condom has not become brittle. Carefully open the condom package, squeeze the air out of the tip, and roll it on gently. Never reuse a condom. Never double up on a condom because the friction of the two condoms will destroy it and there will be no protection at all. Never use a condom that has been left in the car, wallet, or purse because heat, cold, friction, and objects destroy the condom. Never put anything but a water based lubricant on the condom because oil or petroleum based products will destroy it.