Oh man! I love playing with my bf balls, and he loves it even more haha
A lot of times I'll initiate sex by slowly kissing the sensitive areas on his body, especially his neck and ears (seriously, if your man has sensitive ears he would LOVE some tongue action and kisses there), and meanwhile I'll start massaging his balls. So he has sensation in his privates, while receiving strong sensations in his upper body. And also, when I'm doing that I'm either to a side, or right on top of him, so he has a perfect view of my breasts, while I grind my hips into him too. Sometimes while all of that is going on he'll pull my shirt down and start sucking on my nipples.
During oral I also massage his balls whenever I can, and even gently suck on them, or lick them.
Every man is different, but these are things my bf loves to death so maybe this will help any ladies that aren't sure how to handle balls!