Follow up on last post

In my last post (If you didn't read it) TL:DR I said I was straight but wanted to experiment w/ Gay sex. Thanks to the advice I got here I found another person who is experimenting and we decided to get a third person to fulfill my fantasy of being creampied from behind and his of having a threesome. I have zero experience in this, it was just a whim that I decide to experiment, never done any anal play or given oral or anything. My question this time is, what is the best or just some ways in general to prepare my mind and anus for anal sex?