It is hard to recommend a book without knowing how well you speak English. I wouldn't recommend a particularity complex book to a beginner, do you understand? Here are a few of my favourite books:
The Little Prince by Antoine de Saint-Exupéry. This is a very simple book. I have read it in Chinese about 20 times. It's wonderful and talks about how when people grow up, they often forget what it really important in life. Difficulty - 3.5-4/10
The Curious Incident of the Dog in the Nighttime by Mark Haddon. This is about an autistic teenager and how autistic people see the world very differently to us "normal" people. It's wonderful, I thoroughly enjoyed it. Difficulty - 6/10
Matilda by Roald Dahl. One of my mum's favourite books It's about a very clever school girl. Difficulty 5/10
Charlie and the Chocolate Factory by Roald Dahl. I'm sure you know this book! Difficulty 5/10
Animal Farm by George Orwell. This book is about communism and how it doesn't work. It's set in a farm and uses the farm animals to construct a working model of communism and demonstrates how it never works. Difficulty 6/10 (but this book is short!)
The Fault in our Stars by John Green. This is perhaps the best book I have ever read, and definitely one of the saddest books I have ever read. It's about a girl with lung cancer who is depressed and doesn't really want to live anymore until, one day, she meets the love of her life at a cancer support group. They go on a wonderful adventure together to Amsterdam in Holland, and it has a very sad ending (I don't want to spoil it for you)!! Difficulty 8/10
Harry Potter - I'm sure you know these. I highly recommend getting the audiobooks of these is you can, read by Steven Fry. They are AMAZING. He reads them so well. Difficulty 8/10