most reactions change from guy to guy. Some will moan a bit, some will be completely quiet, some touch you, some don't wanna force you down or anything so they keep their hands to themselves for a bit. the one thing I've found that tends to not change is that their abs flex a bit and their muscles in their thighs, ass, and stuff tend to get tense. But you can usually count on a guy to tell you when something isn't working for them. If he doesn't tell you to stop, its good :)
Well in with my experience, he might moan a little bit, make small noises, push down on your head with his hands, and things like that. But, if he didn't enjoy it then he probably wouldn't want you to do it again so that's probably your best clue. If he asks you to do it again then he must have some what enjoyed it the first time. Lol
You can easily tell by the expression on his face... and most guys will let you know if it's bad pretty quickly...
a good way to tell is to take you mouth off it for a while and stroke him... you can judge by how desperate he is to get it back in there!
Really any guy is going to enjoy a BJ some girls are just better than others. If you want him to really enjoy it just make sure to clean up( with out a towel )
Scroll Down to Read Other Opinions
What's Your Opinion? Sign Up Now!trust me...guys like all bj's. some are just better than others...its depends on who is giving it and how much the guy likes them.
if he caresses your head
If he bust his nuts in your mouth You did a Great Job!
Sexual Relationships 
Sexual Health 
Most Helpful Girls