Some of the collectibles have changed from the original (aka switched to a new location), so I have made a new video for the Definitive Edition.
To max out the ability tree without having to grind a lot of enemy kills, you'll want to play on Easy or Normal and get all 33 of the Ability Cells scattered around the world. The video below shows all 33 Cells. However, you should get this achievement for your first ability upgrade very near to the start of the game, as you'll 'level up' your first time just by killing enemies and grabbing spirit orbs.