What powered skills translate best to glider?

If you train in power, I suggest doing so in a taildragger, it'll teach your feet how to fly as well as the rest of you. Nosewheel aircraft tend to make for feet lazy in rudder skills, ground operations and landing in crosswinds. Not saying nosewheel won't do the job, but taildraggers are best - and unfortunately much harder to find instruction in.

Soaring is more about energy management than is power flying. The best thing you can do in a power plane, to relate directly to soaring, is haveing your engine quit. A normally less than enjoyable experience which is typically less traumatic if you have a glider rating.