Hi mak,
The answer is in your position keys.
Theres 2 things to do.
If you stop your figure moving on frame (eg)20, copy that position key and paste to the next frame. (21). (double keying)
Then, if you want him to start moving position again from frame (eg)40, then that 1st key on frame 40 needs to be a 'corner key'.
Doing those 2 things will stop any unwanted position changes between frames.
The same rules apply to anything that doesn't stop moving when you want it to. eg: If you have an arm that is to swing forward and stop, then you would 'double key' his arm bones at the end of the movement, and corner key the frame where you next want his arm to start moving.