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. Be prepared for rejection.
Editors receive thousands of unsolicited manuscripts.
Know the advantages and disadvantages of small and large presses. Submit your best work intelligently. Know the submission process. It is not easy to have a manuscript accepted. Love your work.