After creating your player and starting Career mode, every match you win will earn experience points. Disable the auto save feature. At Junior level, you will start earning 50, 70, or 100 experience points per match. You can accrue the points of two or three tournaments and you can spend them in the player area. When you finish improving the desired areas, save the player improvements and exit Career mode without saving your career progress. When you play Career mode again, the tournaments you played to improve will be there to be played again, as well as the player improvements.
To easily max out your skills, first create a player and win some XP points. Go to "Player Area" and select "Player Evolution". Highlight a skill and press X to add the XP points. Then press X again and remove the XP points you just added. The XP you just added to the skill will remain and you will get the XP points back. Repeat this until all the skills are maxed out.