First of all i like that the giver is caring enough about an anticipate experience to reach out to others in an effort to make it the best experience possible. i like that caring aspect of it that you have.
I like during a bj that if you feel your mouth needs to take a short break, maintaining my arousal with your hand is good. If you want him to cum in your mouth, make sure you communicate so he does not ejaculate during your use of your hand instead, like the combo of signaling to you or your detection from his reactions that he is about ready.
Try to be cognizant of your teeth to minimize contact with them, that the contact should more be with your tongue, lips, & inside walls of your mouth.
Yes, i like my balls & scrotum to be caressed. Once you know this secret & you want me to cum sooner instead of later, the right manipulation of my balls & scrotum would result in me cumming when you want me to. I'm sure every male is different, but if you neglect my scrotum for 5 to 10 mins after around the 20 minute mark, & then resume around the 30 minute mark, i'll cum almost instantly. So you could control when the ejaculation happens based on you knowing what turns your man on.
A few other things i like is varying the speed with which you move your head, & if you vary the technique with perhaps some shaft licking with your tongue outside of your mouth..