The key is to use longer exposures that will not be fast enough to "stop" the action. If you have a camera with a shutter priority setting, you can achieve this by setting a speed that is slower than what the camera would normally program. Similarly, you can also set your f-stop/lens opening to as small as possible, thus increasing the shutter speed needed to obtain a correctly exposed image. Use a tripod if you can or steady yourself on a railing or wall to elminiate camera shake.
Good luck and most of all have fun!

