I am often emailed by new illustrators, asking for advice on contacting publishers. However, it's really important that the folio you show is exactly right. So, before you consider your work ready to show, here are some fundamental things you should check:
Characterisation is paramount.
Picture books are always totally character-lead and those characters have to be ones that children can believe in and take to their hearts.
Some illustrators specialise in either animals or children, but since you are starting out and want to maximise your appeal, try both young children and various animals characters.
You must also show a wide range of emotions, not just 'happy'. Picture book characters will go through adventures where they might need to be angry, lonely, jealous, miserable, cunning...
Draw them doing real things too, not just standing around. Try giving them everyday tasks that get them interacting with their environment and other characters.
Creating individual 'worlds' for them to inhabit is also very important. Look at the range of picture books that are being published at the moment for inspiration.
It helps to illustrate a specific story. This not only gives you ideas, but will demonstrate how you interpret text, which is just as important as your drawing ability. Traditional tales or nursery rhymes can be an easy starting point for experimentation; they will give you a subject matter to interpret, and will not be too hampered by existing illustrations.
A few other tips:
1 - Only put in work you are really proud of: quality is more important than quantity. You need between 10 and 20 pieces, but there should be no padding.
2 - Don't try to be all things to all people - decide what style of work you are best at and then perfect it.
3 - Put your best illustration at the very beginning of the portfolio, and your second best at the very end: that way you start with a bang but also finish on a high note!
Picture books is a lovely field to work in, but hard to break into and requires research, careful targeting of your folio and a lot of determination. Once you are certain your work is right, here's how to get a publisher to look at your new folio.