How to conquer Key Signatures

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#.