Finger in his butt ?! Need advice!

Itll be his first time having that part of him explored other than by doctors, and I plan to be slow and gentle. But how can I make it pleasurable for him ? The first time, should I not even enter, but just touch around ?

I was thinking of making sure he's in the mood first like rlly rlly heated up and getting closer to orgasm, like while I'm blowing him.

Any tips? What do you lovely ladies do ?