To prevent getting a sexually transmitted disease (STD), avoid sexual contact with anyone who has symptoms like genital sores, rashes, or unusual discharge. The safest way to have sex is to be in a monogamous relationship where both partners have tested negative for STDs for at least six months. The USPSTF recommends regular screening for infections such as syphilis for those at higher risk. Using condoms is essential, but avoid those with nonoxynol-9 as they can irritate and increase the risk of infection. To prevent spreading an STD, get tested regularly, inform your partner if you test positive, and always use protection during sex.