DD1 adored the ones like Where is the Green Sheep and The Very Hungry Caterpiller when she was younger - she is now getting into the Dr Seuss and some more complex books. She loves the ones that she can memorise and "read along" with mummy so if she can predict the words from the pictures and/or the rhyme she enjoys them more.

So I guess
- an interesting/funny story or one that she can relate to
- simple words with or without a rhyme depending on the pictures
- pictures that relate to the story