Hey, hello! I just finished two books! Very easy reading, maybe will help you. Easy e shortest books! Forrest Gump (yeh, the book) Bird of Happiness (some tales very shortest asn wise) Try these two, then, if you like, I can send you more tips!

If what you are looking for is a textbook, then i highly recommend all the Oxford ones. You have probably already heard of 'Vocabulary in Use' and they're useful indeed, but the structure itself is a bit monotonous, therefore you can better check Oxford's 'Word Skills' which covers more variable topics (and more colorful, by the way). Talking about books only for reading, I'd rather recommend you to use them for recalling the material you already have in your head since it's quite hard to enjoy a story and look up every word at the time.

I think if you want to improve your vocabulary better use the movies with the subtitles.

Withpering land - Gerrald Durrel

We don't know your english level; still here is what I have found to be the best way to learn words, it's Etymology. Yes, when you learn words through their etymology you won't forget their meaning. For instance, 'psyche' means 'mental' and 'gene' means 'birth', 'beginning', and 'origin' knowing this you can figure out what "psychogenic" means. Of course, "psychogenic" means something of mental origin. Now if you know that 'pathos' means 'disease' you can figure out what "pathogenic" means. Again, of course "pathogenic" means something that gives birth to disease. Can you tell me what "psychopathic" would mean?