Reasons could be:
1. Your trying to hard. Relax! Let go! Don't concentrate as hard as you can.
2. Your thinking about how it works. Forget logic and science for the moment you are trying telekinesis. Just know its possible.
3. Your expecting results to soon. If none of the above things work, it may be because you are inpatient. Take your time.
Good luck! I hope this helped!