Don't skip steps in your developments, there are no short cuts to tennis mastery.
Have a vision for how you want your game to develop. You will hit many roadblocks along the way just like Rod did. In the beginning he struggled with strength on his backhand, then consistency. His backhand took years and years to develop, however his vision for what the potential results could be kept him focused and determined.
When you are ready hit with players who are a little stronger than you.
Once your game is developed learn how to play under pressure. Rod liked to keep his opponents guessing by being aggressive on big points.
Be disciplined in your practice. Learn to improve your accuracy under pressure. Practice drills where you have to hit in certain areas of the court under pressure.
Make sure you get your body physically strong enough to be able to execute all the skills and movements in tennis.
Analyze matches you watched. For example if a professional like Federer lost a big match in a 5th set tie-breaker, try to figure out why he lost. What could he have done different to change the outcome of the match?
Practice at an extreme disadvantage when you know you are going to play someone with a big weapon and learn how to get comfortable returning that shot. For example, Rod's story about practicing returning serves as his partners were pounding serves at him from inside the baseline.