Brush your underfinger on the bottom of the quilt to feel the advance your needle. You feel the tip skip over the whorls of your fingerprint sooner than the pressure or prick of the needle so you can rock your needle down a thread sooner but still be confident you've really got the backing. Your fingers won't be sore or get callused (much.)
Instead of coming back to just perpendicular, keep going another 10 or 15 degrees so that you feel like you are taking a bit of a back stitch.
These are the tips I used to get up to 10 st/inch and I was really thrilled with my bad self. I had to really concentrate to do it. I don't see myself ever doing 12. I use Kona solid quilt a bit, so that's 60 threads to an inch. That means I cross three threads on top and supposedly three threads on bottom. I don't usually catch my bottom stitch fully. Okay. I never catch my bottom stitch fully. And I usually relax and make myself very happy stitching 8 st/in.
One thing I'll throw in about preserving your hands, I use spring loaded jeweler's flat nose pliers to pull my needle through. I know it's awkward, but I also know nobody at my LQS hand quilts anymore because they all--yes, she told me all of them--all got some kind of thumb and joint pain from furiously gripping the needle to try and pull it through by hand. I've gotten very speedy with my pliers.