Making sure you have your own business plan is key, because this is a business like any other. Doing 'the best work you can do' is a maxim or a mantra, not a business plan. We'll take it as read that you are producing work of the highest quality, what you have to learn to do now is present it properly, to markets that want it. I have long believed that selling cartoons is a separate skill from creating them; which is why so many cartoonists hand that job over to someone else. If you don't want to do that, then you have to learn the art of selling your work.
If you are like me, and like Mike, you'll still draw cartoons and illustrations on paper, so making sure you have all the materials you'll need, at your disposal, is essential. Currently, that can be quite an expensive business and it involves several pieces of hardware, a computer, a scanner, a printer, and software, Photoshop, Paintshop Pro, Painter, Flash, In Design, Acrobat, Quark, many cartoonists have all of these, and despite many still drawing their cartoons with pen and ink, they also have digital tablets and pens, principally Wacom tablets, because they are the best.
On the drawing front, I keep (so obviously I think it's a good idea to do so) a regular supply of the following; a range of papers, HP typing paper, Conqueror typing paper, tracing paper, Neenah Linen paper (from England via the US), Strathmore Bristol Board (from the US), Ivory Board (from Switzerland) and Marker pads. I like FW Acrylic inks because I can use these with dip pens and they also fill Staedtlers, Rotrings, Koh-I-Noors, Pental Brush Pens and, if you prize the lid of them, Faber Castell-Pitt artists pens. I also use Sakura Pigma Micron pens and Staedtler felt tips and grey Prismacolor Markers for toning (on the recommendation of Mark Anderson). A bunch of nibs (I have become more and more reliant on Japanese nibs as the range is superb) pencils, elastic erasers, sharpeners and rulers.
Just click the messy scene above for a clearer picture