Dresden Files: GASP
Called shots can be performed in two ways.
One is that they are the result of a maneuver. You take aim for a spot, then tag it to target a specific location. This does not grant any bonuses to the hit, but allows you to gain any bonuses the location might imply. If it is unarmored, then they do not gain the protection from the armor for example.
Second is a success with style. If the attack succeeds by three or more you can choose to invoke a called shot as the benefit.
Spin & Style
A successful defensive roll by three or more generates spin, this is an optional rule in the books but is being implemented here. Spin provides a +1 bonus, or -1 penalty to actions taken to or against this character respectively until the end of their next turn.
Success with style is any actions that succeeds by three or more. By doing so the person usually gains an additional benefit, depending on the situation.
Any maneuver, action, or roll, no matter how well or poorly rolled must make sense in the context of the world or scene.
Example: A roll of 9 on a might check is amazing, and mighty your character is, but no pure mortal can ever lift a tank over his head and throw it.