Play a major scale in the key of C (no sharps or flats).
Play a Mixolydian mode ascending in the key of C but beginning with the note G. (A Mixolydian mode is one that is based on the 5th of a major scale. Thus, if you were playing a C Major scale with no sharps and flats, you would start with the 5th of C, which is G if you count C as 1, D as 2, E as 3, F as 4, G as 5.)
Add a flatted 7 note as you descend the scale by determining what note is the next to the last one on the ascension. (In the Mixolydian mode in the key of G based off C major, you would count C, D, E, F, G, A, B, C as 1, 2, 3, 4, 5, 6, 7, 8. Flat the next to the last note -the 7- which would be B, adding a B flat.)
Play a major scale in the key of C (no sharps or flats).
Play an Ionian mode ascending in the key of C. The Ionian mode adds a chromatic note after the fifth note. Thus, in the scale of C major you would again count C, D, E, F, G, A, B, C as 1, 2, 3, 4, 5, 6, 7, 8, the fifth note is the G.
Raise the G a half step to add a G sharp to add to your scale.