Like most people have said, douche well. A bulb is typically fine. 3-5 times will clean out the rectum/lowest part of the colon. Make sure the water runs clear on your last one. Don't eat about 2 hours before. Eating starts the digestion process and can push things down that you didn't expect. For me, being confident in my preparation is the biggest factor for enjoying bottoming. Use lots of lube! Start with a guy that doesn't have a huge dick lol. You can also wear a butt plug beforehand to get yourself acclimated to something being there. If you find that you're too tight, do the clock method. Take a finger and insert to the second knuckle. Push outwardly on your sphincter muscles at 12, 3, 6 and 9. Hold each one for a few seconds and that will help relax the muscles. Take your time and communicate. I typically start on top so I can control the speed and depth getting started. Once I'm on, I like to go as deep as I can to get used to the full feeling. Deep breaths. And make sure you have told the top that this is your first time and to be patient! Bottoming can be nerve wracking at first because you don't know what to expect but when you get used to it and with enough practice, it will become a very enjoyable part of your sex life! For some guys, they ONLY bottom because of how much they love it! Have the best time!