Three things:
Relaxation
Preparation
Don't sweat the little stuff.
I've been a top and a bottom and I enjoy both when it comes to anal sex. Anyone that's done it enough knows that sometimes there is a tiny bit of poo, unless the bottom takes a enema first, which ruins the spontaneity for me. It isn't a big deal, it's how our bodies work. If it happens, don't sweat it, condoms come off and bodies wash.
Lube is vital, if it's dry it will hurt, even for those of us with a bit more experience. Same for the top taking time to prepare the bottom and, being aware of the bottom's experience, or lack there of. I'm sure you've at least read it in gay fiction, the lube up, one finger, then tow, then maybe 3 thing. Well, especially if you are new to being an anal bottom, that is very important for your partner to do for you.
As others have said, using butt plugs to stretch yourself gradually is also a big help when you are just starting to get into anal.
Some guys simply never enjoy anal and, it certainly isn't required that you do just because you are gay. There are a lot of other ways to pleasure each other and, if anal isn't for you at all, or if you only enjoy beads or small plugs, that's fine too. Experiment, see what you do enjoy, and try some of the things we have all mentioned here.
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In my opinion the phrase "if it hurts you're doing it wrong" really does apply. Use lube, go slowly and try different positions. It helps if the top can be a little more on the sensual side of things rather than "I'm gonna pound ur ass guy". Poppers can things easier and make the pleasure more intense but they come at a price and long term use can create problems.
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First of all, anal sex is not the only thing two guys can do. Secondly have you ever heard of foreplay? Try it, it's better than sex and certainly leads to better sex. Don't be in such a hurry, there is more to having sex than pump,pump come!
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I completely agree with Lambert on the foreplay thing. It's what makes the follow up intense and rewarding. I can easily see how doing only pump, pump, pump ..... and eventually coming could be uncomfortable for the bottom, or a bit of a chore for the top. It's all a question of balance between comfort and timing.
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