Where you feel the stretch might vary, but if done correctly you will stretch all the relevant portions of the muscle. Hold this position for 20-30 seconds, feel a tension in the forearm. Be sure to keep your elbow straight throughout. 

How many how often?

Try doing 3 to 5 exercises at a time, holding for 20-30 seconds. You can repeat this again at intervals in the day.

What is the benefit of this exercise?

This exercise mainly stretches the muscles over the forearm which originate from the common extensor tendon at the outer aspect of your painful elbow. The stretch generates a useful stress on the tendon to assist healing.

What can I expect to happen?

You may feel a stretch in your forearm and wrist. Sometimes some discomfort in the outer elbow at the tennis elbow pain-site when you release the stretch. All of this is normal. 

Works best with?

eccentric elbow exercise, thoracic rotation