The first lesson is often the most informative and we will get a solid grasp of your skill level, fitness, strengths and weaknesses as well as just getting to know one another as the personal aspect is often the most important.
Once students have all the necessary shots and not only an ability to play but an understanding of how to play we can move on to the minutia of what students are interested both in terms of shots and theory. Students often are interested in learning how to hit a roll vs flick or an off-speed speedup with disguise. Students also frequently choose to work on entirely new shots like changing from a one handed to a two handed backhand drive or a scorpion counter. From here the options are limitless and only directed by what I think would be useful skills for their play style and their personal interest to pursue those or other skills.
Once all the basics are squared away I truly believe in self direction from students. People often excel only at what they want to which is why interest from the student is critical to whatever aspect of the game they are working on. The most common choices for students are thirds, including both drops and drives, dinking, reseting in the mid court, and handling pace off of opponents drives and speed ups. Students at this point are also introduced to more complex theory on court positioning, shot selection, shading, ready position, and exploiting weaknesses.
The second and third lessons are often best used to address foundational aspects of play that, without doing properly, can stop you from progressing further. The common issues I find that can be fixed easily are the grip, basic court positioning, mentality, and understandings of basic strategy.