I was actually disappointed first time I got a BJ. Same happened with my 5-6 next girlfriends. I just thought that whole thing is overrated. My cock hit the teeth, their mouths were dryish and they gagged easily; and worst of all, didn't let me to cum in their mouths.
Then suddendly, I met my ex gf and she literally blew up my mind. Where I it took unbelievable long time to cum with my ex gfs, this girl could easily make me cum in a minute. The best of all, she loved to do it unlike the girls I had met earlier. She sucked me every time we had sex either during the foreplay or to finish me off. She was also willing to fullfill my somewhat porn distorted fantasies by wearing loads of make-up, false lashes, smearing my cock with lipstick and salivating so heavily it dropped on the floor, which made the experience even better.
As expected, after breaking up with her I'm now expecting too much of blowjobs and usually get disappointed. Sometimes a really good looking face can save it though.
In a nut shell. Good blowjob is half skill, half anatomy. I've noticed that girls with big mouths, big tongue and thick lips give much better bjs in average (black girls <3). Interestingly, you can also hear and see from girls speech how wet her mouth is. I'd also avoid girls with piercings, some people like them but normally they start to irritate me very quickly.
Well, happy bj hunting.