You can view the skill tree at any time by pressing or at the end of the levels. There are 5 different "branches" to the tree and you will need to fully upgrade every ability, which will cost 3 skill point coins each. After 1 playthrough you should be about halfway through this achievement. The quickest episode to gain skill point coins is episode 1. You gain around 5-7 coins in this episode so it shouldn’t take too long. Rick needs 60 Skill point coins to fully upgrade whereas Lori needs 66.
Avoiding The Glitch
If you are playing this in single player with Lori there is a chance you may not unlock this achievement. A glitch can occur when you complete all episodes and complete the game. Completing the game will cause the abilities in the "talent" section of the tree to auto upgrade. This means you won’t be able to upgrade them without deleting your data and starting over. To avoid this you can either play in co-op, or make sure you spend your skill points on this section of the tree as soon as possible, to stop the game from upgrading them for you.