Record everything. Curate nothing.
Your rating is built from every shot the system has ever seen you play. A full, unedited session tells it far more than a highlights reel could. There is no penalty for scrappiness. Warm-ups, drills, games that got away from you: it all counts, and honest footage is what makes the rating honest.
Matches and practice are different evidence, and both matter. Competitive play shows how you behave under pressure, which is what Initiative and Composure listen for. Practice shows repetition and technical shape. Record both and the picture fills in from both sides.
Length. From about twenty minutes, a session is well worth uploading. An hour or more is ideal. A handful of shots processes happily; it just moves your picture slowly.
What the camera needs. The court, the ball and you, framed as described in Where to put your phone. What it cannot use is footage from a phone being carried about. Set it and leave it.
The players whose ratings sharpen fastest are not the best players. They are the ones for whom pressing record is as automatic as zipping the racket bag.