Planet 51

Very simply, presses the “X button” while in a Blue square and then press it once more when the meter is inside of the little BOX section. If done correctly it will say in the corner of your screen “PERFECT” throw. Do this for all 15 throws and the achievement will unlock. Subsequently if you mess up you can replay the mission from the main menu, or attempt it in the “Glipforg Newspaper Boy” task.