When introducing my wife to anal sex I found tapered toys very helpful. The Tantus Champlette is particularly well suited because in addition to being tapered it has a smooth - not matte - finish silicone that slides easily with the proper amount of lube. As others have said - you can never have too much lube - or patience. For a while we also used a lube shooter to get more lube inside which will facilitate penetration and thrusting. We don't need that any more.

Vibrations also help. The Tantus B-Bomb is a modestly sized silicone butt plug - again with the smooth finish. Although I am slightly larger than the B-Bomb, once my wife is comfortable with me stroking the B-Bomb in-and-out, she can handle me (an average sized guy).

Also caution your guy to pause after entry to allow you to adjust - no thrusting until you give the ok - even then have him start with slow short thrusts.

Positions can also help - at the beginning my wife preferred missionary using a Liberator wedge pillow to align me with her. Others suggest the cowgirl position (girl on top) because you can control the speed, depth and pace of penetration. Others like spooning - find what works for you.

After a few months of regular anal sex the whole process gets a lot less difficult and complicated. You learn to relax and he learns how to do anal sex for you.

Going back to a the topic of patience - I always made it clear that my goal was to make sure that my wife was able to have an orgasm during anal sex. She was skeptical - but it did happen (it took a few months) - and now happens on a regular basis. This makes all the patience and trouble worth the effort.