For me, switching to computer with cadence helped overcome some of my mashing tendencies. I aim a gear that I can comfortably spin at 90-100 rpms.

When I do one-legged drills, I unclip and rest my non-performing leg on the top of the trainer. It helps me rest that leg while keeping it out of the rear wheel I also find that a slightly harder gear provides a little more resistance and actually makes it easier to do one-legged drills than an easier gear.