How do you levitate stuff with your mind?

I'm sure most of you have the same question as me. Well I've been trying for the past hour to levitate something by focusing on the object. One of the objects I tried floated millimeter off the ground/my bed, but then it didn't work anymore! So I'm Trying to find a source online that will teach me. yahoo is only one of the many websites I'm asking. So....? Do any of you know how to levitate stuff with your mind?