Have a trainer show you how to use the arc trainer if you have not used one before. The movement can take some adjustment and you'll want to know how to adjust the machine before going it alone.
Begin in an upright position with both feet on the arc trainer's pedals. Positioning yourself correctly before starting will keep your body in the proper form to prevent injury.
Keep your hips stationary as you move through the arc trainer's movement. This will place less stress on your hips and knees. You'll also get more muscle benefit from the movement.
Place your hands on the handrests or move them as if you are running. Using the handrests gives you greater stability, particularly if you are unfamiliar with the machine. Some arc trainers have movable arms that you can use to target your arm muscles.
Find a comfortable pace and rhythm for your workout. Going too fast or trying to stretch beyond a comfortable point will affect your form and can lead to injury.
Adjust the resistance and incline to a comfortable, but challenging, level. Using levels that are too difficult for you will often lead to improper form. If you want to increase the difficulty, go slowly.