For flat keys, you would first have to memorize this- Battle Ends And Down Goes Charles Father-This is the exacts opposite of sharp keys. Then, you spot your key in there and every note up to it and the one after it is flat in that key. As an example, the key of A flat would have a B flat, E flat, A flat and D flat. F only has one flat , B. You need to remember this one. C simply has no sharp or flats.