A few tips you should know first before you try Anal Play
Hygiene- Overall hygiene is great and pay attention to your nails. if you have long nails try to trim them and wash your hands with soap and water for 20 secs.
Safety - STIs can be passed between SO'S. Always use protection such as a condom or dental dam.
Comfort- Unlike the vagina the booty isn't self lubricating. Try using a silicone lube to avoid painful friction.
Relaxation- Try to remember to go slow this way your muscles won't tense up.