Start gently. Use your tongue, lips, and hands in combination. Focus on the frenulum (the sensitive area on the underside) and the glans (the head), as these remain highly sensitive areas.

Ask what terms they use for their body and what kind of touch they enjoy. Some may have "bottom dysphoria" and prefer not to have their genitals touched at all, while others may be very comfortable with it.

Using condoms or dental dams is the best way to prevent STIs.