When you learn how to draw caricatures, you will want to observe your subject and see what features make the subject recognized. For example, your father sometimes has a big nose; Noses are very popular features used for exaggerating caricatures. The features that you choose to exaggerate should have features that make your subject recognized.
Caricature vs. Portrait?
The biggest difference in caricature and portraits is that a cartoon is almost a cartoon version of the person. A portrait is more of a realistic view of the person. When you start learning how to draw caricatures, you want to use people you know. You also need to have a good understanding of the basic layout of the human face. Techniques such as proportions and shortening can also be very practical. Any technique that you learn to draw people can be used in an exaggerated way when drawing caricatures.
See the topic!
Being able to see the topic "in the round" is the best way to get a whole sense of the subject you are drawing. You will also want to recognize some features that can be minimized as well. Not all features are exaggerated in a way that makes them big, but you can also make them very small. For example, if you draw a person and they have a small mouth, you can make it even smaller in the drawing. This is a kind of reverse exaggeration.
Dumb it Down!
You will also want to "fool down" some features. For example, the hair is often "dumbed down" because you don't want to pull either hair in the caricature. This gives the image more of a cartoon-ish look compared to a standing look.
Simple drawing rules apply to learn how to draw a cartoon. Do not overdo features that are not typical or easily recognized. For example, if your topic doesn't have a big nose, don't give them a big nose. Work with features that can be exaggerated without making the person unrecognizable.
A cartoon is a cartoon, if you say it is!