Here I set out a formula for introductions and endings for songs. I don't claim this to be the only method to use,
but it is easy and useful for any song in any of the 12 keys in the chromatic scale. You have to adjust for #s and bs!
I will use the key of C to demonstrate my formula: This system, abridged or not, can be used for turn arounds too.
The formula is the very one which is the progression in a vast number of popular songs, i,e., I, VI, (II or IV), V
chord(I) of root note -> chord (VI) of note 6 -> chord (II) of note 2 or 4 (chord IV) -> chord (V) of note 5:
First chord of the root note - I use either the Major .or the Sixth which may be shown as I.maj or I.6 (roman figures)
Second chord is built on the 6th note and here are some examples: (VIdim, VI7, VIm7, VIb7)
Note: G# is also Ab, so the formula still holds since half tone variants can be used to great effect in Jazz.
Third chord is built on either a 2nd or a 4th notes of our scale - In our example we could choose a D or an F chord
here are a few offerings. I like minors or minor 7ths or variants of 7ths eg 9ths, dominant7 #5 or minor7 -5.
Fourth chord is a 7th of the 5th note (V) = G. Mostly the dominant is used but I like variants here too.
but you can always play two 2 quarter notes in the final barre by adding another (optional) chord for a different effect.
The above 4 measures will give you an idea of what it might all sound like.