For advanced spell casters, while pulling the control stick in the direction you want to pull, wiggle it around that point. You will find that your Carpe Retractum spell is faster at pulling. The best place to try this is the Prefect's Bathroom.
After the third task, when Harry is alone against Voldemort, you first must kill all the skeletons, before and after you link wands. When Voldemort is hurling the statue at you, dodge it until it gets stuck in the ground for a couple seconds then hit it with the giant ball of light that is coming from the wands. Repeat this until all the limbs are off the statue and you will win.