This article by Sarah McIntyre was written in April 2016 but it's great information for both writers and illustrators. It popped up on my twitter feed today.
'Can you illustrate my book?' Some tips for writers approaching illustrators
https://jabberworks.livejournal.com/744387.html [10 February 2016]
As well as being a illustrator, she has a lot of knowledge to share. Check her website out to see her portfolio and her live journal for more of her articles and goings on. Sarah is also active on the usual socials!