1) In which position did you give/receive your first anal sex?
We used one of the classic positions- doggy or ass up/head down positions.
2) Which position would you recommend for the first anally?
Well for the first anal experience for the one being penetrated, I would say have the receiver lay on their back and put a pillow under their lower back which elevates their hips and makes their anus more accessible for the penetrator.
Another good position is doggy style which does make penetration relatively easy.
One position which is often used by experience players is to have the one receiving the cock is to be on top and basically sit on the cock. This gives the receiver full control of the penetration and lets them go at their own pace vs. the penetrator taking the lead.
Now positions aside, there are several things that should be done prior to a cock entering an anus especially for the first anal experience.
The receiver should clean their ass- anal douche by way of enema, shower shot etc.
The penetrator should insert fingers first and relax the sphincter muscles before penetrating.
Definitely use lube. My favorite is coconut oil but absolutely use lube on the anus and the cock.
If you make the first anal experience an erotic one for the receiver they will want to come back for more! A win-win for both of you.