Giuseppe Castellano is an art director at Penguin Random House. He recently started a blog with illustration advice.
There is a lot of terrible advice out there for beginning illustrators!
If you want to illustrate as a full time occupation, it is made up of all kinds of jobs, not just some Platonic ideal job that will make your career. I know a lot of artists who routinely turn down work that is not precisely what they want to do and they suffer; eventually taking a job completely unrelated to what they want to do because that rent bill is not going to pay itself.
Giuseppe's post is the best advice I have seen in a while. Check it out!
My favorite quote (and I have actually told people this in the past):
"When discussing this topic with my wife, she said it better (and in
fewer words) than I ever could, “It’s like saying ‘I’m holding out
for Lear’.” She went on to quote, “There are no small parts, only small
Sometimes a small job or something that seems at first glance not what you would ideally want to do may be the springboard to an amazing job.
He compares illustration to plumbing but it really is more like bricklaying to me. Sometimes you are building a small house, sometimes it is a high-rise condo but it is still built one brick at a time.