The following tips should help you with your panning attempts:
1. Start tracking the subject as soon as he/she/it appears on one end of the frame.
2. It's usually a good idea to release the shutter as the subject reaches the middle of the frame (of course, you could do it a bit later or earlier but might miss the frame).
3. After the shutter has been released, keep panning along with the subject, this usually helps provide a very well patterned background.
4. Keep shutter speed as slow as possible and the highest f-stop that you can manage.
5. The backgrounds are an important aspect of a panned photo, so look for contrasting colors and patterns.
Remember that panning is a semi-advanced technique so don't worry if you dont get it perfectly in the first few attempts. Keep trying you'll end up with a magical shot very soon.