The players who train with a purpose and know exactly what they are working on and build a plan on how to improve that area and then execute that plan are the players who improve the quickest.
Many players show up day in, day out and work on the same things, train the same way and their progress is very slow.
I have been lucky enough to have been around top players training on a day to day basis and I have witnessed how each day these pros come out and train with a purpose and the improvements are massive.