If you're referring to coaching juniors, I couldn't reach ~90% potential in all stats in master difficulty so I gave up with trying to coach a junior starting player.
I did find though that you want to play tournaments at least 2-3 times in the first year, increasing by 1 or 2 every year for better motivation and experience for building the mental skills up. Make sure you enter both singles and doubles, even if you don't intend on doing this as a pro because the experience you gain helps out a lot, and if you get a good partner you can win a couple of matches easily no matter how low your own skills are which helps self confidence and motivation, which in turn helps you win more singles matches.
Also, bear in mind that your topspin will start at 5%, so enter indoor/grass tournaments while it's still low to give yourself a better chance of winning at the start. Winning matches is very important for motivation which, as far as I'm aware, helps you train more efficiently, and so will help you get better potentials.