Drawing cartoons is a lot of fun. I've been drawing since I was old enough to hold a pencil, or a crayon, and have always found it to be a pure joy. My dad used to bring home reams of computer paper from work for me to draw on when I was a kid. Yes, I drew on both sides, my mom insisted on it! In school I drew cartoons of all of the adventures of my friends. I was a very shy kid, and drawing cartoons helped me to make friends.
If you would like to make money drawing cartoons, I would say the most important thing to focus on is to follow directions. That is, the specifics about what your client wants. It's all well and good to be fabulously talented, but that doesn't mean anything to a client who wants a cartoon of penguins and you give them bunnies!
Seriously, listen to your client. Nowadays most of my clients write emails to me with what they want, and I print the emails out and put them in front of me while I am drawing. This, of course, doesn't mean that what they are asking for is ALL that you give them. You are supposed to be creative here. If your client is a self-storage place, then maybe they will suggest a couple of business people surrounded by files, boxes of stuff, maybe a basketball. Be sure to include all of those things! That is the first thing that your client will look for. If you disagree with whether businesspeople would store a basketball, that's a completely different issue.
I recommend giving your client what they are asking for. If you are an artist, draw. If you want to argue, become a lawyer or something. Double-check your sketch against the request your client made. If you forgot something, go put it in before you show it. If your client asks for something else after they see the sketch, draw it. That's what the sketch is for. When you are paid, and submit the final artwork, the transaction is complete, and everyone is happy.