Sports Fitness Advisor Tennis Training Section: http://www.sport-fitness-advisor.com...-training.html
Note that in their program they strongly advise against jumping right to explosive plyometric exercises without first developing a strength base - otherwise you risk incurring an injury.
The Elite Approach to Tennis Strength Training http://www.sport-fitness-advisor.com...-training.html
Also note that they strongly advise a shoulder and forearm program to help prevent the common overuse injuries that plague tennis players.
Although several exercises are listed on their site, I think the best of these shoulder and forearm program is the Thrower's Ten Exercises: http://www.muhlenberg.edu/pdf/main/a...throwers10.pdf
Also, as you get closer to your season, consider increasing your "running". Here's what one USTA coach recommends:
"When training the players the USTA works with, we usually do some sort of "running" four to five times a week. The running session usually lasts between 20 – 40 minutes, but there is a lot of variety in the types of running we do.
You’ll note that we put running in quotation marks, because much of what we do is different from the long, slow distance running many tennis players are familiar with – there is some long distance running, but the “running” sessions also involve footwork/tennis agility work, or interval runs. The type of running depends upon the periodized strength and conditioning schedule of the player.
Generally, the long distance running and longer interval repeats (400s and 800s) are done during the preparation phase when you are getting ready for the season. Shorter, higher intensity intervals (20s, 40s, 60s, 100s, 200s, and 400s) and on-court footwork/tennis agility are the main focus during the pre-competition phase in the weeks leading up to main competition or competitions. During the competition phase of the season, on-court footwork/tennis agility is the “running” focus.
Recognizing that each player is an individual, we adjust the plan depending upon the player’s cardiovascular endurance, agility and their physical and physiological strengths and weaknesses."
Agility Drills http://assets.usta.com/assets/1/USTA...oc_437_269.pdf
High Intensity Interval Training (HIIT) http://www.intervaltraining.net/hiit.html
You can do those agility drills using a HIIT-like approach, and even add in swinging before each change in direction like on spider drills and horizontal repeaters.
Good footwork improves when it is your sole focus in a drill, without also having to concentrate on tracking the ball and hitting it.