I found it common in illustrated storybooks to have large visuals, and smaller (though not too small) text. It’s made obvious a lot of the time that we are supposed to be focusing our attention on a main or focal point of the page. A standard, easy read font is usually commonplace as well, being Helvetica, Times New Roman or the such.
However, due to having a subversive nature in my project I’ve decided on a rather unattractive text, and a quite unnatural visual to text ratio (however, one may conclude my text to be illustrative in itself anyway).
Text is usually placed in clear view, though not so much a hindrance to the illustration. The good thing about this is because these are literally the only two solid elements on the page it’s almost quite simple to format it well and creatively. And with such a divergent book as mine is, I’m hoping to experiment extensively with format and text.