I'm sure you'll get an illustrator response soon, but here are some basics from an author. Your SCBWI region may have an illustrator coordinator who can help you find critique partners, workshops, and places to look for general advice. (If not, ask the RA if there are illustration groups or events planned.) It's also important that you practice your craft. Sketch as often as you can. Loose sketches are fine as starters. Start to figure out what you're good at and what needs work, so you know how to build on your strengths and weaknesses. Even if you can't get a degree, you may find inexpensive courses for continuing education students at universities and libraries or online.
Another tip is to copy the masters. Look at picture books and think about how the illustrator composed each spread. Consider line and color. How was the tone achieved? What parts speak to you and why? Conversely are there any illustrations or styles you don't connect with? Why? This can help you hone in on your own style and on what works and what doesn't in general. Take a page of text and create you own vision of it and compare it to the original.
A Google search for illustration blogs may also help. All of these can help you grow as an artist. Knowing when you're ready to put your work out there is harder to judge, but critique partners may help with this. Hopefully, I've given you a start to your journey. Enjoy the ride!