You have probably heard of the so called "Circle of 5ths". Consult Captain Fantastic's blog for some info on it:
http://www.guitar.com/greighgripearce/blog/the_circle_of_fifths
 
 
So why am I making this blog, if the 5ths have already been discussed?
To point out some "rules" behind the concept of the circle that will hopefully help you memorize it and recall and use it easily.
 
So I created what I call the "Star of Fifths" . It is a stripped down version of how the Circle of 5ths is usually presented.
 
The notes are laid around in a circle, exactly as is the case with the circle of fifths. But I display the info differently.
I don't overlay the relative minor keys as they are redundant and make it seem like you have to memorize more than you actually need to. Instead, I draw an arrow from one major key to it's relative minor. Doing so, revealed that 3 rectangles are formed. Reading clockwise within any one of the rectangles, each point is the relative minor key of the preceding point (functioning as a major key). This also organizes the notes in 3 groups of 4 notes easy to memorize and recall. No need to pull the entire Circle from your memory to find a relative minor key. All you need is the appropriate rectangle.
The other thing I do differently is the use of flats and sharps. Lower complexity makes things easier to grasp. So I display everything as natural notes or sharps of them. No flats. We're trying to get a basic hold on things, not get admitted to a philharmonic orchestra ;-P Plus it makes it easier (for me) to memorize. Go ahead and display them as you think it best helps you. I provide a flats version further below. But finding the flats when you know the sharps is easy.

I'm showing here the Circle with flats as well. I'm also adding the two "missing" sharps from the order of sharps, which I omitted purposedly in the first Star. The notes are the same, it's only the name that changes. Personally, I could live with just the first version of the Star.

An interesting thing about the Circle of Fifths is shown in the following image. Although the note (say F#) on the opposite side of the circle from a given note (say C) has no significant meaning, the notes flanking it have. Counterclockwise is the Cb and clockwise it is the C#, This is true for all 12 notes displayed on the circle. This may help you remember the Circle and fill in the blanks. Captain Fantastic's blog (link top of this page) has another mnemonic rule for remembering the order in which notes are layed along the circle.

 
Two things you need to know about how the Cicle is built:
1) Immediately ounter-clockwise of each note you'll find the 4th of its major scale and immediately clockwise of it you'll find the 5th of it's major scale. Blues,pop,rock,country songs often rely on those 3 chords a lot.
A result of the above is the order in which the notes of a major key are organised. Reading clockwise the order is "4th root 5th 2nd 6th 3rd 7th". You'll need this when you look for 3rd or 7th etc in a certain key. It will be easier to remember if you note that it consists of '4567' intersected with '123' to produce "4152637" . The minor key looks more scrambled: "6 3 7 4 root 5 2" (strictly that would actually be "b6 b3 b7 4 root 5 2" in proper terms, because notes are typically always numbered after the major key of the same root).
2) The third note clockwise of any given major key root, is the root for its relative minor key (the minor key with the exact same notes as the given major key). Backwards, the third note counterclockwise of any given minor key root, is the root for its relative major key.
 
 
A few examples on reading the star:
 
1) Finding the relative minor key: The relative minor of Cmaj is Amin, as indicated by the arrow linking these two. The relative minor key of Amaj is F#min. The relative minor of F#maj is D#min. Finally, the relative minor of D#maj is Cmin, and thus the first rectangle is formed.
 
2) Finding the notes of any major key: Starting one note counter-clockwise from the root note, read clockwise 7 notes. These are the notes in your scale. For Cmaj this translates into: F, C, G, D, A, E, B. Put in order they are CDEFGAB(C).
For Amaj that means: D,A,E,B,F#,C#,G# and in the proper order: ABC#DEF#G#(A)
Using the 4152637 rule you can put them in order quickly or directly retrieve any specific one note out of a specific key.
3) Finding the notes of any minor key:
Trace the arrow backwards to the relative major key.
The notes in the relative major key are exactly the same as in the minor key you're after. Look at the previous example on how to find the notes of a major key.
So the notes for Amin are all the same as the notes for Cmaj, but ordered to start on A.
The correct order rule here is 6 3 7 4 root 5 2 for the aeolian (natural minor) scale.
4) Finding the 5th and 4th in a given key: The 4th and 5th of a key are very popular in blues and rock (and not only) when building chord progressions.
In a given key (say C) the 4th is found immediatelly on its counterclockwise side (here it is F) and the 5th is found immediatelly on its clockwise side (here it is G).
Enjoy!
- RG -