Picture
How to work out any major scale that starts on a flat (b).
(for example Db major, Eb major, Gb major, Ab major, Bb major).
Rule 1: If there is one flat in the key signature the key is F major

Rule 2: If there is more than one flat in the key signature the second to last flat is the key e.g. Bb Eb Ab = Eb major

Rule 3: To find the key signature (if you have the key) go up to the key note in your rhyme plus one more in the rhyme;
          Battle Ends And Down Goes Charles Father.
 e.g. Db major= Go up to Db in the rhyme "Battle Ends And Down..." plus one more in the rhyme ... "Goes". So Db major= Bb Eb Ab Db Gb 
 
Picture
How to work out any major scale/key that starts on a white note;
(For example C major, D major, E major, F major, G major, A major and B major)
Rule 1
We have to remember that C major has no sharps(#) or flats(b), only white notes.
And F major has a Bb.

Rule 2
Find your key note (the note your scale would start on) then jump back one semitone(one step) to find your last sharp, then add in all sharps before it in your rhyme;


FATHER CHARLES GOES DOWN AND ENDS BATTLE

e.g. D major (jump back gives you C #- FATHER CHARLES)
So D major= F# + C#
       E major (jump back gives you D #- FATHER CHARLES GOES DOWN)
So E major= F#, C#, G# + D#.