Straddle the belt with each food on the stationary outside deck and start at a strolling pace of 20 minutes per mile or less (3 miles per hour, if that is the calibration used).
When the belt is moving smoothly, step on and walk at that pace until you establish the rhythm of your walk and feel totally relaxed and coordinated.
Increase the belt speed gradually over several minutes, always making sure you have your posture, technique, and rhythm in sync.
Increase your heart rate with walking speed rather than by elevating the treadmill. Try to walk fast with the treadmill flat or only elevated a few degrees to get your heart rate up. If you are unable to do that, then elevate the treadmill to the level of a gradual hill and increase your heart rate by walking much slower.
Don't hold the handrails. If you have to hold the rails to keep your balance, you have the treadmill going too fast relative to your walking ablility.
At a brisk pace, and particularly at an aerobic pace, walkers must have a good loose arm swing to counterbalance their faster leg swing. Just as important, a vigorous arm wing involves the major muscle groups in the upper body that would be inactive if you were holding the handrails.