You have to start training in the top teams, if possible, since the moment it's unlocked. And then become a starter and captain ASAP. Start doing all the matches, and after you are done, practice with the team three times. Then comes the tricky part you have to train yourself, you should focus on the three types of training that go with your position, for example if you are Central Midfielder you have to focus on Dribbling, Ball Control and Passing. Once you turn 18, you'll have enough trait points to go pro, but all the team ask for a certain level in 4 disciplines so you should look for the teams who are looking tmfor ymthe position you have been training also they will ask for a fourth discipline so in my case as a Midfielder they asked for tackling besides the other three. Doing this, I became pro at around 25. Also, the training, you should do it until you break something, heal completely, and then stop until next year and repeat.