Try Drinking Coffee
Try drinking coffee the morning of the big day. There's a good reason that. There are coffee mugs that say, "Coffee makes me poop." Next, if you have bullets in the chamber, poop them out before anal. A good bowel movement and a cleaning with simple soap and water is an easy way to prep.
Should I Use an Enema?
To enema or not to enema, that is the question. If the act of pooping and cleaning up the exterior isn't enough for you, an enema may be the next way to go. Buy a disposable enema kit from any pharmacy. Also, use plain warm water. You don't need to use a cleansing solution.
Relaxation Is Key
Relaxation is the key element needed to prepare for anal sex. Relax both your mind and your body. Use methods like massage, touch, and lots of foreplay. Once relaxed it's time for lube. Lube is a personal preference. I prefer silicone lube for anal sex. It's more slippery, needs less reapplication, is hypoallergenic, and safe to use with condoms. Feel free to use water based (thicker is better), oil based like petroleum jelly (you can't use condoms with this), or a hybrid silicone/water lube.
Getting Started With Anal Sex
Start by either using a small butt plug, anal beads, or even a finger. Gradually use larger toys or add more fingers until the ass is relaxed and ready for larger toys or penile penetration. It is important to get as turned on as possible. The hornier you are, the more enjoyable the anal sex will be.
Now that you are clean, relaxed, horny, and lubed you are fully prepared for anal sex. Have a great time, stay sex positive, and have great anal sex!