Many times tennis elbow, or lateral epicondylalgia is the result of overuse of the tendons around the outside of the elbow. Painful tendons tend to respond well to eccentric loading.
Eccentrics, or negative workouts, are a great entry point to start working on ROM and strength.
In this video we start with forearm lowering with the hand in neutral. The right hand helps to bend the left arm up and then you slowly lower the weight down. The lowering phase should be about 3 seconds. Do about 10 reps and then do a set with palm facing up and a set of 10 with palm facing down to target all the different muscles around the elbow.