I have been making a living as a "street" artist (caricature and portrait artist) for 23 or 24 years, who's counting. I wanted to look into doing something else art related to make extra money in addition to the caricatures during the slow periods.
I picked up this book based on reviews and I thought it may be helpful. Well I thought it was outstanding. The author is an artist working in the field, so she understands that most of us artists hate the yucky numbers and business stuff! She spells it out in such a way that even people who may not enjoy such things can understand and even find them interesting. You can be the best artist in the world but fail at the business because of these pitfalls.