You might think that fucking a guy is pretty straightforward, but if you want to be a great 'top' (the guy doing the fucking) it helps to know how the arse works. So before you start banging away, follow these tips.

Unless a guy is relaxed and ready, fucking might be a painful for him. Taking the time for foreplay will make fucking much more comfortable. This can include rimming, gentle fingering, lubrication, patience and listening to each other and responding appropriately.

Find out what he likes
Being a top isn't about being dominant. It's true that some guys like to be dominated but not everyone does. Don't just charge in there. If you ask him how he likes to be fucked you can try and fulfil his request, if you like the sound of it. Listen to his reactions too. If he is making noises that suggest he's in pain, try to move more slowly. Most guys like a change in rhythm now and then so variation is good, but if he's screaming with joy, keep doing what you're doing!

Getting hard
The first time you fuck someone, you may be a little anxious. This can sometimes make your erection less hard than usual. Remember to relax – you're both there to enjoy yourself. If you have problems with your erection just concentrate on something else, like kissing, for a while. It can also help if you ask the guy you're having sex with to do something you like, whether it's sucking your cock or playing with your nipples. 

Using plenty of lube will make fucking easier and safer. Use water-based or silicone-based lubricant if you are using latex condoms (oil-based lube can break them). Avoid using any lube with nonoxynol-9 in it, as it can irritate the lining of his arse, and this can make transmission of HIV easier. 

Different guys like different positions so it's worth experimenting. If you've been fucked, you can think about what you enjoyed and try that out on the guy you want to fuck. Not everyone is the same but it's a good place to start. Any position where his knees are bent and drawn into his chest (whether he is kneeling, lying on his back or on his side) will probably lead to a more comfortable fuck. This position will allow smoother entry to the arse. Once you've got the hang of that you may want to change and try something else. This will help your cock to stimulate different parts of his arse, giving new sensations. Remember to listen to his reactions or ask him if he likes it. Some positions may be uncomfortable for you or him.
Tops at risk
Remember that the guy doing the fucking can be at risk of getting HIV. It's not as risky as getting fucked but it's more risky than oral sex. This is because anal mucus that lines the arse (we all have it) can contain a very high concentration of HIV. The mucous membrane just inside the tip of the penis and the foreskin can absorb liquids, like anal mucus, directly into the bloodstream. So if you fuck a guy's arse without a condom, any HIV in his anal mucus could enter your body through the end of your cock. Using condoms and water-based or silicone-based lube for fucking will help protect you and your partner from HIV and other STIs.