Skintones / Histogram

I'm currently working without a light meter. I have two AB800's, and my current method of setting exposure is simply to shoot RAW, view my histogram and make sure I'm not clipping either end. I use a gray background, so that helps as well as far as viewing the histogram (I think).

My question is, assuming I shooting fair skinned caucasians, where should the skintones land on the histogram, or in Lightroom. I tend to land around the 80% mark in Lightroom for skintones. And I also tend to adjust plus or minus a half stop in Lightroom as well.

I know about Chuck's white towel method, and I know I should get a white/gray card as well.

In the meantime, how should I eyeball exposure?