Default is for suckers: How to unlock full skill tree customization in Diablo 3
Diablo 3 has a secret. It won't tell you, but you don't actually have to select one skill from each of the categories (Primary, Defensive, etc.) that it forces on you. You can pick any seven skills in your entire arsenal for your active set, but that capability is disabled by default. We show you how to enable it in 10 seconds flat.
Step 1: Click the Game Menu button or hit Escape.
Step 2: Click Options at the top of the list.
Step 3: Open the Gameplay sub-menu on the left side of the UI.
Step 4: Check the box labeled Elective Mode in the bottom right.
Step 5: Click Apply and exit back to the game.
Step 6: Right-click a skill in your action bar. You can now use the arrows to select Skills from every category.
Step 7: Celebrate your new-found freedom with gratuitous demon-slaughtering.