My husband became accustomed to it by me straddling his face when I got home or licking it off my stomach. I don't normally like guys pulling out, so this had to be prearranged.
From what my husband said, the whole bj experience is just "different." There's no real way to simulate it. When he finally did give his first bj, he said it was so different than me sticking a strapon in his mouth. Then, when the guy came, he said it was "on another level." He knew he was going to swallow, but he said when the guy started cumming, he kinda froze for a second, then started to swallow. His first bj guy came a good amount.