If you want to practice holding an intention, practice on your own body where you can get instant feedback, and do stuff like will your body temperature to change, or will circles to appear on your arms, and will sensations to happen, and so on. Also practicing mediumship is good, try putting out your hand and willing that an entity takes control over it temporarily, to write out a message to you. You just let your hand sit there with the pencil in the hand but 0 nerve force being exerted to hold it and you wait, you hold the intent, until it is stirred into action by something other than your own will.