As you observe others stair stepping you will quickly notice a variety of styles. Choose a speed that you can move smoothly with the pedals. Don’t try to force the pedals down or have it set so fast that you are at the bottom of the machine. Step height should be comfortable. Don’t feel like you have to take large steps or take such small steps that your knees barely bend.
Stair stepper training is the only mode of cross training I have been able to find in the medical research that actually improves running times without increasing the amount of training. Researchers compared “physically active” college age women who trained only on a stair stepper to a group that ran. After nine weeks of training four days per week, beginning at thirty minutes and increasing to forty five minutes, the running group improved 11% and the stair stepper group improved 8% on a 1.5 mile run. It must be noted that the participants in this study were “physically active college women,” as opposed to competitive distance runners in the swimming, cycling, and deep water running studies.