Once you are happy with the blocking of your animation the next stage is to add inbetweens and make sure all your keys flow smoothly into each other. In CG animation this is refered to as spline as it is the process of converting your stepped keys to spilned keys in the graph editor.
Spine process:
Timing refers to the number of drawings or frames for a given action, which translates to the speed of the action on film. On a purely physical level, correct timing makes objects appear to obey the laws of physics; for instance, an object's weight determines how it reacts to an impetus, like a push.
The movement of the human body, and most other objects, needs time to accelerate and slow down. For this reason, animation looks more realistic if it has more drawings near the beginning and end of an action, emphasising the extreme poses, and fewer in the middle.