Hey Friend,
I mentioned I had a little process I used to figure out a scale based on a particular key. It's nothing elaborate, just a way I keep things straight in my head.
Regardless of the the key, I always keep C major as the reference. Remember, key of C major is all natural notes (no sharps or flats), so if I can remember the order of the notes and the intervals (or spaces) between each, all I have to do with a new key is shift notes as I need to.
And I shift them based on the pattern: W W H W W W H
Wanna try another key? Let's look at D major.
I start with my reference - C major. The intervals between each note will always be the same, and note order is easy to keep track of - just remember the alphabet.
1 2 3 4 5 6 7 8 C w D w E h F w G w A w B h (C)
Shifting to D major:
1 2 3 4 5 6 7 8 B w E w F# h G w b w B w C# h (D)
We've got the note order down (right?) - D E F G A B... All we need to do here is shift the notes appropriately to determine which ones became sharp (or flat).
The space between D and E will always be two frets. If we look at the scale and the pattern, D to E is a whole step, so that fits.
E to F should only be one fret, but looking at the pattern, we need to have a whole step for the D major scale. There you have it - F needs to shift up one fret to become F#.
One cool thing about using the Circle of Fifths is that the sharps are cumulative. We started with G major, which has one sharp - the F# note. If you look above at the key of D major, you now have two sharps. And look at that, F# carried over from G and we added C#.
Those are both of the notes that are a half step interval in the key of C. Just an observation - I don't think there's any significance to our understanding of learning keys.
Gotta go for now...
Peace~
Dave | 
