Right after a match or training session is a very important time to stretch. Players bodies are still warm and they increase there range of motion and flexibility, while also helping there muscles recover better. It is normal for tennis players to get tight glutes, hip flexors and hamstrings after training. A lot of lower back injuries are caused from tightness in these areas. In addition, increasing the range of motion in the shoulders is very important in performance and injury prevention.
Some important post training stretches are shown below. They should be held for around 30 seconds. It's good to have a MM stretch strap or MB Stretchband, but tubing can also be used and wrapped around the foot for assisted leg stretches.
The pigeon stretch is also very good.
Hip Flexor Stetch
Sholder Stretch (sleeper stretch)