Major Key Signatures Handy Guide Theory Things   William Wieland
Sharps:6012345
 F  C  G  D  A  E  B 
Flats:1065432

Explanation
        F  C  G  D  A  E  B 
Write the order of sharps. Eventually, this is all you will visualize.
Sharps:012345
 F  C  G  D  A  E  B 
C major has zero sharps. G has 1 sharp. D has 2. A - 3. E - 4. B - 5.
Sharps:6012345
 F  C  G  D  A  E  B 
Continue counting on the other end. Add "sharp" to the letter. F sharp major has 6 sharps.
The order of flats is the order of sharps backwards. We number flats backwards.
Sharps:6012345
 F  C  G  D  A  E  B 
Flats:10
C major has zero flats. F major has 1 flat.
Sharps:6012345
 F  C  G  D  A  E  B 
Flats:1065432
Continue counting on the other end. Add "flat" to each letter.
B flat major has 2 flats. E flat has 3. A flat - 4. D flat - 5. G flat - 6.