Create systems for jotting ideas and images. Consider taking writing workshops, attending conferences, and forming a writing group. Cultivate the habit of revision. The many books about writing help this essential habit. Know about publication if that interests you.
Some writers find it helpful to know what's being published.
They read reviews of picture books and browse in bookstores. Understand that picture book publishing is a collaborative process. If you need total control of the process, best publish your own manuscript. Know that publishing is a business. A publisher has to believe that a manuscript will sell when it competes with 5,000 others.