With grinding for me, what seems to work is Push-Pull. I'll grind for a bit, but pull away and start dancing on my own or with her friends, as most girls dance with their friends, talk to her friends, etc.. It messes with her a bit, she'll usually come up to me and pull me back in. If not, I'll pretend that i'm not paying attention to her, walk away a few feet, talk to other girls or her friends, then re-engage her after a few minutes. The key is to not to too overboard on the grinding. I see guys do this and it ends up looking needy and desperate.