Dani Jones will tell you! Read her fantastic article "How to find an illustrator for your picture book". All I can say, (while enthusiastically nodding up and down) is "What SHE said!"
It's brilliantly concise, well-written, thorough, and, yes folks, it is all true. Dani knows the scoop, explains it in plain english, and leaves no stone unturned. (The girl knows how to communicate.) Read it... But please don't weep! Digest the information, stick the priceless info in your virtual 'back pocket', and move onward and upward forward with your amazing creative career.