Which advanced chords can I use for a song composition in scale of G?

Question

I am making a song composition in a scale of G.
I have already used major chords G, C and D and in some places I have used Am, Em and Bm.

I would like to make this composition richer with some advanced chords?
I am not a guitar expert. I know that we can add Gsus, Cadd9, etc but not sure about their exact application
So I wanted to check with you guys to know whether anything else can be added to make my composition better.

If someone can provide with some thumb-rule or formula, that would be even better..

Thanks in advance.
Jeril

Answer 1

Use the diatonic harmony trick of stacking notes and see what you come up with.

For instance, in G, the notes of the major scale are

   G  A  B  C  D  E F#

If we stack every other note in that list (wrap to the beginning when necessary) 3 times we get a simple minor or major chord/triad:

  G,B,D    - G  Major
  A,C,E    - A  Minor
  B,D,F#   - B  Minor
  C,E,G    - C  Major
  D,F#,A   - D  Major
  E,G,B    - E  Minor
  F#,A,C   - F# Diminished

If we stack 4 times we get a more flavorful chord:

  G,B,D,F# - G Major 7th
  A,C,E,G  - A Minor 7th
  B,D,F#,A - B Minor 7th
  C,E,G,B  - C Major 7th
  D,F#,A,C - D Major 7th
  E,G,B,D  - E Minor 7th
  F#,A,C,E - F# Diminished 7th

You can keep stacking but at a certain point things become pointless. 5 stacks usually ends up in some kind of add 9 chord with the third and seventh chords in the list becoming a flat 9 (9th lowered one half step).

If you have a song in a minor key, use the corresponding minor scale to do the stacking.

You can take the above and do chord substitutions as well, such as the 5th of the 5th sub and the tritone substitution.

Here's a more complete explanation of diatonic harmony based on the major scale and here's one based on the minor scale.