You'll need access to the Black Emporium and enough gold to afford the Maker's Sigh potion, which resets all Ability Points/Attributes. Hawke's unique preset skills mean that when you use a Maker's Sigh potion and save, the preset skills will be always be filled. Perform the following steps to easily gain ability points:
1. Use a Maker's Sigh.
2. Save your game and reload the file.
3. Examine your Ability Points; you should see the amount removes plus Hawke's preset abilities. For a Rogue this will be 4-5 points in the fual-wield tree.
4. Use another Maker's Sigh to add those Abilities to the Ability Points. Repeat this as many times as desired as long as you have the potions, just make sure to save and reload the game each time.