The basic idea behind panning is that you pan your camera along in time with the moving subject and click the subject while you follow the subject.  So we get a relatively sharp subject but a blurred background.

This gives the shot a feeling of movement and speed.

Tips for Panning:-

• Use shutter priority mode when freezing the motion (Tv for Cannon and S for Nikon)
• Use the auto focus of your camera if the focusing happens fast. Make sure your focus mode is set to AI Servo so your camera continually focuses as you pan your subject. (AF - C on nikon)
• If the lens is not focussing fast enough, you can use manual focus and make sure you have subject in focus where you intent to click before making it Manual. 
• Keep ISO low at day time and increase it a bit at night time.
• Do some practice shot first to find out the correct shutter speed required.
• Select a slightly slower shutter speed.... Normally it should be in proportion with the focal length...For Example:- If you are shooting at 50mm then your shutter speed should be slightly less than 1/50 sec to get the background blur effect..
• Make sure your shooting mode is continuous. So you can click multiple shots when you are actually panning the subject. 
• When all settings are fine, you are ready to take panning shots. Make sure you review the photos to check the subject is completely crisp and nicely focussed while making the background blur. 

Keep practicing and have fun :)

Do let me know if this blog was of any help and do share this blog with your friends as well :)

~RJ