Make use of arcs
One approach that will take your animation to another level is the use of arcs. In the natural world things tend to move in arcs. Balls travel in an arc to the ground. Butterflies tend to float in a series of overlapping arcs. Playing with the concept of arcs through space (X, Y and Z axes) will give your scene a much more dynamic feel.
Animate on 2s
The eye perceives individual frames as continuous motion and a standard theatrical film has a frame-rate of 24 frames per second. Life-like animation is animated on ‘2s’: we hold each image for two frames. In most cases 12 unique drawings for each second of your scene is enough. However, for faster action for example, you may need more drawings to achieve smoothness.