This is an older article that I just saw by a guy named Ken Rockwell. It's called How to Become a Professional Photographer. It's long, but worth a read if you are in early stages of considering starting just about any business. He talks a lot about how the important part of running a photography business is the actual business side rather than the photography side. Also, about how important sales and marketing are. I've thought off and on since I probably about that time I first picked up a camera about having a photography business. I've worked directly for a few photographer and with a bunch more and freelanced myself for a while. From everything I've seen, the article pretty well nails it. Perhaps my favorite quote is up towards the top:
Would you like to photograph anything you want, anywhere you want, anytime you want, any way you want, with a great professional camera system? Would you love to travel to luxury destinations and photograph whatever, whenever you want? The only way to do this is to keep your real job and do photography on your own time.
I haven't been shooting much recently, but I couldn't agree more.