"NASA? You mean the National Anal Sex Association?"
Where to start?
First of all, I'd like to say that regardless of how heavily the media portrays anal sex as a popular act, it is a huge exaggeration. It's not nearly as popular as something like PornHub would lead you to believe. Although more and more women are being open about it, it's not safe to make the assumption that anal is expected from a relationship.
If you have talked about it with your partner, and you’re sure that this is something you both want to try, please don’t be a baby. One partner of mine started talking about anal after we had slept together a few times. I told him I wasn’t prepared for anal and had not given myself an enema. He seemed almost puzzled, as if assholes are just naturally spotless. It may seem obvious, but poop comes out of there.
There’s also the assumption that anal is just for guys, which I can say is totally wrong. I prefer anal over vaginal sex at times. As monkeyxxx from reddit stated, “If you have kind of a big penis you can stimulate the G-spot while doing it anally. Granted, her comfort level is the most important thing and lots of lube and anal foreplay are required, but that's part of the fun. Talking dirty about what I'm gonna do while playing with her asshole is a psychological bonus. My girlfriend has intense vaginal orgasms from anal sex. She asks for it and it's a regular part of our sex life. Starting from the side position, just sticking the head in and then kissing her neck and softly playing with her hips and nipples for 5 or so minutes seems to bring the hip action from her. Slow and sensual. Not all out anal warfare like all the brain dead porn depicts.” And it is a very different feel, not what you’d expect from it.
The key is to warm up for it and make sure you’re ready for anal before you try anything. This is important for guys too. If you want your girlfriend or fuck buddy to continue giving you anal sex, don’t think with your dick. Take it slow, make sure everything is a-okay, and especially lubed up. I’m telling you from personal experience here. When anal sex hurts, it REALLY REALLY hurts. It’s a stinging, stunning pain that persists. There is no quicker way to ruin the mood for me than an inexperienced yet eager partner who wants anal without the warm up. It’s just not meant to happen, sorry.
Above all, you want to remember that it’s supposed to be fun. A lot of women are really worried about accidentally ‘making a mess,' but in all honesty you’ll be able to tell if you are/are not ready for anal. Eating fiber helps, regularly going to the bathroom helps, and if those fail an enema is always an option. Good luck, I hope that most women can experience an anal orgasm at least once in their lifetime, but considering some women never even orgasm vaginally, we might have a ways to go!