(This will work better if you can actually hear when something is a major scale and can adjust a note that is off)
Play a C major scale. C,D,E,F,G,A,B,C (all the white keys)
Now go 5 piano keys over, which will be a perfect 5th, from C to G. This is also the span of your 5 fingers.
Since you're on G, play a G major scale. If you can hear what a major scale must sound like, you will have sharped the F for F#. The key of G major has one sharp - F#.
Go up 5 again to D. Play D major. To make it sound right, you also have to sharp C#. Now you have two sharps in the key signature - F# and C#.
If you keep going up a perfect 5th, you'll have A major, E major, B major, and each time you are adding another sharp to the key signature. You will have your "Father Charles".
I never memorized these sayings, but they do reflect the order of sharps:
G major - F#
D major - same, add C#
A major - same, add G#
E major - same, add D#
B major - same, add A#
Notice also that the sharp you add to your previous collection of sharps is always a semitone below the tonic (F# below G, C# below D etc.)
If you were to write in the sharps in the key signature of E major, you would write them in your Father Charles order, in two diagonal lines.