The thing with bottoming is the pleasure builds up over time. The first few minutes something is back there it might hurt a little bit and it might feel like you need to use the bathroom. But the hornier you get and the more you stimulate your anus and prostate the better and better it feels until it builds up to a point where youre getting this incredible sensation that radiates from your prostate through your whole body. You just need to get over that initial hump of awkwardness and discomfort.
What really helps is prep, prep and more prep. Use the bathroom, take a shower, do a quick douche if youre worried about making a mess. And abstain for a few days. You want to be as horny as possible. The more horny you are the better it will feel.
Before hooking up with a guy, try practicing on your own. Buy some dildos or an aneros if you can afford it. Next is to get comfortable. Lay in bed in a comfortable position. and get to relaxing. Because the prostate sensations are subtle at first if youre tensing up your other body parts or youre not comfortable it will be hard to focus on the feeling you want to build on. Next, take it really slow and use lots of lube. If youre not used to anal, rushing things or being tense back there can make things painful. Next, load up some porn and go to town. Explore the sensations. Some guys have their prostates further up, some closer to the exit. Explore and see what works for you. Try different positions, different angles, different sizes of toys different rhythms. That way the next time you see a guy, you know exactly what to tell him to rock your world. Thats also another key thing. Communicate, communicate communicate. Let him know if you want him to go shallow, deeper, slower, faster. Tell him what works for you and you both will have a really good time.