I just got asked this on Facebook and it’s a variant of a question I get asked a lot and I usually just write out the same answer over and over again so today I’m copying and pasting my answer into a blogpost so I can refer future askers to the answer here!
It really is a how to get to Carnagie Hall situation! I highly recommend Tom Richmond’s Mad Art of Caricature for concepts of caricature that you can then apply in a live setting. I also did a workshop with Tom last year that changed my game overnight so highly recommend attending next time he’s running one. After that it really is practice. A lot of people get hung up on their drawings not being immediately “good”, you really have to put that aside and push through it or you’ll never get started. I also recommend you study the proportions and structures of the head, this is really foundational (and I should probably have started with it!). To this end I recommend Stephen Bauman’s Headstudy app. Daily thumbnail studies of the head will give you a solid sense of what everything is and where it should go under there. After that find and follow professional caricature artists on their socials and really try to study what they’re doing.
I have an earlier blogpost on this very subject based on some handouts I created for caricature workshops a few years ago. I don’t do workshops any more but the principles are solid.