My wife had a few partners before we got together - she was 26 and was good with her tongue at licking and teasing but not what you'd call an expert at giving a bj. This didn't really matter as she is a small frame with 36DD tits so a lot of the time my cock was titty fucking her.
Anyhow, as the years went on I wanted her to be able to deep throat as it's a useful skill for a wife to have. So, one day, we both got naked and I lay her on the bed on her back with her head hanging over the side. I then stood by her head and over the next 30 minutes or so used that position to help her relax and get used to my cock going deeper and deeper into her mouth.
It was a good position as it gave me easy access to play with her tits and finger her sensitive clit to keep her aroused. Anyway it wasn't long before I was balls deep in her mouth and she handled it easily.
Since then she loves a good mouth fuck - likes it quite rough and looks amazing taking my cock all the way down - I'm about 6.5" but confident she could handle bigger!