It took me ages to master the deepthroat, with many bad experiences, but here's what I did:
I got my bf to lie on the bed, and I gave him oral from the side, kneeling at the side of the bed, if that makes sense. He's really long, and quite wide, so if I tried simply facing him, it was just too wide for me to deepthroat. But from the side it was so much easier, it just went right in!
Also, if you wanna practise on inanimate objects, I suggest trying to find something bigger than he is, so if you kinda even half-master that, it'll be much easier during the real thing! But nothing beats practising on the real thing, and I'm sure he wouldn't mind either
All I have to say is "I wanna practise that thing..again" and he's undressed