Oral sex

So I was with my ex for 2 years and we just recently broke up about a month 1/2 ago. We’ll call him (B). B was not circumcised, which was fine with me I didn’t mind. I got used to having sex with him and giving him head etc.

well my other ex before ex B, we’ll call him (M) he is circumcised, and when we were dating I never gave him head. Anyway I just saw ex M the other day, and we had sex and I finally gave him head. But I feel like I was doing a really bad job, and I felt kinda lost in what to do. And he didn’t seem like he was enjoying it very much. Has anyone else experienced this? Or can give me more tips or anything?