With each new sexual partner you have, your chances of getting an STD increase. The only sure fire way to avoid an STD is not to have sex. This is true if you are only having sex with them, and they are only having sex with you. Using a latex condom decreases your chances of getting an STD but does not eliminate them. Many STDs can appear on parts of the body that is not covered by the condom.
Transmission is possible when the infected area rubs against the other person.
The final way to reduce your chances of getting an STD is to recognize the common symptoms. If you notice the symptoms in yourself, you can prevent transmitting it to someone else. If you see the symptoms on your partner, you can question them about it. Some STDs can have no symptoms. Any sores, blisters, or rashes especially in the area that pubic hair covers.