Children's books are good to start with and work your way up from. Especially popular or older ones which are available in translation that you can compare against. You can also try finding French translations of English books you have read and enjoyed once you think your vocabulary is up to it.
You might want to give a try to this temporarily freebie offer (DRM-free ePub & Mobi):
French Masters by Delphi Classics is a collection of public domain works which includes both the English and French versions so you can check your understanding of the story.
Hope this helps.