>>40279389 (OP)lay down a towel just in case (you won't regret it), and use COPIOUS amounts of lube. as soon as things are remotely uncomfortable for either of you, apply more to both your dick and her hole.
if it's her first time, go as slowly as you can. finger her first, insert inches at a time so she can get used to you. even gentle anal can cause bleeding without any training, this is natural but you should be as gentle as possible and stop if things hurt. use your words and make sure she's comfortable as you go in deeper and speed up.
goes without saying, but make sure she cleans out beforehand, wear a condom, and don't expect anything. it was already mentioned, but foreplay and aftercare are key. don't neglect the rest of her body either! treat her right <3