Like people already said, there's a big importance of knowing how to draw the face. No matter how good you can color, your final image is still going to look wrong, since the basis is wrong. So if you want to improve your coloring skills you'll have to improve your knowledge about anatomy alongside. Your drawing seems like a nice start. If you were asking me, I would exaggerated is forehead instead of his cheeks. Because is the boldest feature of his face in my opinion. The coloring is nice, it can be seen that you have an understanding of volume and forms, but you'll have to work on drawing anatomy correctly. There is an amazing caricature artist I very admire, here is a link to his blog: [link] his name is Jason Seiler. I learned a lot from his works, I bet you can learn a lot too. Moreover he teaches at Schoolism.com caricature. So if you're planning to sharpen your skills more in the future, you can enroll to his course. You can find in his blog some good tutorials. Good luck
I would say before worrying about painting a caricature you should focus on being able to just draw a caricature. If you can't draw it then no amount of painting can help.
Caricature is a lot like life drawing in that it requires a good amount of observational drawing. The real difference is that where life drawing is about capturing the forms and dynamics of what you see in real life, caricature is about exaggerating those forms and dynamics. You should just try doing normal observational sketches of people and then doing variations of those sketches that exaggerate the most noticeable traits about the subject; and not just making their jaws and noses huge (not everyone has a prominent jaw/mouth/nose).
You could also try analyzing the works of classic caricaturists to get some ideas on how to go about caricature (I don't mean jack someone else's style and pass it off as your own, I mean really analyze). Some good artists to start research on would be Miguel Covarrubias, Al Hirschfeld, Olaf Gulbransson, Jack Davis, Mort Drucker, and George Grosz.