For spinning excercises, I'd recommend a higher gear/lower cadence. This will stop your leg from "rolling through" from the momentum of the cranks moving at high speed, and allow you to focus on a smooth movement all the way around. Once you get a good technique you'll be ready to sping quickly, but until then it's probably best to go slower and focus on smooth, steady power. As you progress and become better at spinning, you'll be able to go at a higher cadence and maintain the proper technique.
jmlee is right, you don't actually want to pull up on the pedals- just lift some weight off the leg that is not pushing. This helps spread the work across both legs, because the power leg doesn't have to also lift your other leg. Starting at the top, try to push forward, down, and then pull back- but don't actually pull up- just get the weight off the pedal. Picture a clock, you should start at 11, push forward and down to 5, and then pull back and slightly up to 7.
Good luck!
- Mike