+add as contact
My biggest tip for anal sex is to have a douche or enema beforehand, maybe a couple of hours before playing, it helps ease the psychological fear of "accidents". Doing that for the first time can be a big step for people in itself though.
But if you're trying to introduce the idea, I'd do it in stages, don't even attempt penetration, just play with anal massage, well lubed stroking and massaging of the whole of the buttocks and then the sphincter itself, just around the outside until you feel it relax, it can be extremely pleasurable on its own. And if you're both comfortable with it, rimming.
Do those on a few occasions and playing down there becomes much less threatening, your partner will be much more relaxed and you can progress to a small toy or buttplug. I'd avoid inserting fingers until they are very comfortable with anal, that always feels more uncomfortable than a toy or a even a cock. The thing about starting with anal sex is that it is as much psychological as physical.