Go to Yurindo!
I always go to Yurindo when looking for English books. Yurindo is a chain book store that is present everywhere in Japan, usually near big stations. The one in Yokohama station has a relatively good selection of English books. The books range from well-known classics to popular books that were recently published. If looking for a book you want or just rummaging for a good book to reading during the holidays, I definitely recommend stepping into Yurindo!
If you can't find it here and you know the book that you want, I recommend ordering online at Amazon.co.jp. This would be the best option if you don't mind waiting a day to a week for your book to arrive!