These are the most effective exercises for tennis elbow, when done together. If you are willing to give your condition some time to resolve, and it not in the acutely painful stage, (IE typically, you have had this condition for 6 weeks or more), then give the following regime up to 6-8 weeks of your time.
Tennis elbow stretch. Where you feel the stretch might vary, but if done correctly you will stretch all the relevant portions of the muscle. Typically repeat this stretch 3 times, a few times a day
Side Lying trunk rotation. I find that mobilising the thoracic spine can be very valuable when trying to manage a stubborn tennis elbow. This is possibly because the thoracic spine contains the majority of the autonomic nervous system that exerts some regulatory control on tissue health, or perhaps because tennis elbow can sometimes have a neuropathic or nerve-pain element. Do this exercise 10-15 times on both sides.
Eccentric elbow exercises. Start with a light weight. On a very painful tennis elbow, simply the weight of a rolling-pin might be enough stress to start-with. Just follow the same technique as demonstrated, and build up the weight gradually. Remember, slow and steady wins the race! Try doing this a few times a day in sets of 3-5 repetitions.