How much of a caricature you make will depend on your goal for the drawing. In order to get the likeness, you can keep the features of the subject minimzed or maximized as long as you can keep the likeness. You will have to use your own imagination to create this distortion and exaggerate the features of the subject, by exaggerating the features you can get a likeness.

You can practice on your friends. You can practice on your children, then do a caricature of them. Practice drawing the likeness of your friends with different features. Practice drawing the likeness of yourself, maybe with a bigger chin, or a longer nose, or a shorter neck. So here is the plan.

As you practice drawing a caricature, you will get to an understanding of where you can and cannot go with exaggerating the features of the subject.