There is no book about Flash Memory design as I know of. Read some book about DRAM design instead and learn these techniques. Learn what conditions need to be met for Read, Program, Erase. Learn some techniques how to design diffrent voltage levels from the main power supply and learn some level shift circuitries.
I am working on Flash Memory I/F design currently. And I have a very good design guide I got it from Toshiba. It helps me clear up NOR and NAND type flash characteristics and difference. It also provide some design guide to Flash memory I/F design.