one method that might work could be this, but mind the render time would increase somewhat.
after animating the main object, duplicate it, then offset it by a frame or so, so that it starts moving a frame after the original.
also, reduce the copied objects transparency by a small amount. then duplicate this object, repeating the previous steps of offsetting it by a frame and reducing it's transpancy. of yeah, and add motion blur to these objects.
continiue this so that you have a trail of objects which gradually become invisible. once they are moving, and with the motion blur set high enough, it should produce a nice tail like effect that gradually fades out
like i said, render times for this could be somewhat on the high side, and a post process method would be much more efficient. i would really suggest learning a package like after effects, as even a basic understanding of it can help compliment your 3D work a great deal with the addition of some simple effects.
