only 1 percent to 10 percent of all illustration students will succeed as professionals.
Illustrators that work freelance need to have a strong sense of self-motivation. You will need a good head for business and be very organized. It is good to have a thick skin for criticism and a dogged sense of perseverance. You need to be knowledgeable about your areas of interest and also know how to negotiate contracts and understand copyright law.
Your art skills have to be professional quality with the ability to work fast in both color and black and white. You need to be flexible with making changes at any stage from sketch to final art. Your figure drawing skills need to be top notch. You need to be able to draw people of all ages, genders and types in movement and at rest. You need to be able to draw animals, architecture, costume, landscape and interiors. You also need to develop research skills especially for science and historical illustration.
If you feel that you need an artistic muse or that you often run into "artist's block" then the field of illustration isn't for you. Publishers aren't going to wait around for you to be "inspired".
You have to be willing to keep learning and growing as an artist through all your career. Don't depend on one style of illustration to keep your career going. Take classes, experiment with new media, expand your strengths and keep growing as an artist. Diversify your areas of expertise so that you can survive the vagaries of changing needs and tastes in illustration.
The most successful illustrators are the ones that persevere. They have a good head for business and can work in a timely manner, following directions and being pleasant clients. They can weather the unpredictable nature of freelancing and balance their personal and professional lives.