Not bad for a first try. To make the animation more fluid, you have to set a higher framerate (like 24 or 30 fps). Obviously, the drawback is that you have to *make* more frames *^_^ To do that, you could take this animation, put the frames you already did at regular intervals, and fill the intervals. That's how they do it in traditional animation (= drawing all the frames, as opposed to keyframe animation where the software does the intervals).
If you prefer keyframe animation, you can also create a vector shape of the tail, and move the control points of the shape to let Flash do the interpolation.
I don't mean your animation is bad, it's cute. I just provide constructive criticism in case you have a use for it. If not, you can just ignore my rambling