by Versilaryan » 20 Apr 2012 21:41
Hi, and welcome to MLR! ^^
Your knowledge makes things much easier to explain. So, all chords in a key consist of triads: a root note, a major or minor third above that, and a fifth above the root. Going up the C major scale:
C E G
D F A
E G B
F A C
G B D
A C E
B D F
C E G again
You'll notice that the chords are all major or minor (not counting that diminished chord at the end). It goes Major, minor, minor, Major, Major, minor, diminished, and then back to Major. So, we'll notate that using numbers. Capital letters mean major, lowercase means minor.
C - I
D - ii
E - iii
F - IV
G - V
A - vi
B - vii(dim)
C - I
In a minor scale, you get:
i (C Eb G)
ii(dim) (D F Ab)
III (Eb G Bb)
iv (F Ab C)
v (G Bb D)
V (G B D)
VI (Ab C Eb)
VII (Bb D F)
vii(dim) (B D F)
i again
Technically, you can get a few more by combining notes in the melodic minor scale (like ii or IV), but those just sound weird 'cause nobody uses them. If you're doing something like progressive house that relies on odd chords, it's definitely something to look into. Or you could just use them anyways and make them work. Whatever sounds good.
Next point: how they work. The first note in a scale is obviously the root (called tonic, if you didn't know) -- it's what key the song is in. The second-most important note is the 7th note, the leading tone.
You'll notice that iii, V, and vii(dim) all contain the leading tone. (So in C major, EGB GBD BDF). Not counting iii (just don't use that one -- it ends up sounding weird most of the time), they all lead into the I chord. If you play it on a piano or guitar, just go G major to C major, or B diminished to C major, it resolves. V and vii(dim) are the dominant chords. I is tonic, and all the rest of them are subdominant.
All chords in a harmonic progression go from tonic to subdominant to dominant back to tonic. If you're a nerd like me and harmonically analyze music you hear on the radio, you'll notice a lot of music doesn't follow that. That's what my theory teacher called a harmonic regression, where you go from tonic to dominant to subdominant just so that your chord structure is really easy to repeat over and over and over again. At this point, it's really up to you, though if you try to write an orchestral piece with a harmonic regression, no composer will give you the light of day.
That being said, what you need to do is once you have a melody or a bassline, figure out what chords fit it and then work the rest of your parts around that. If you have a lot of moving lines, make sure that no two notes are ever a dissonant interval apart (seconds, sevenths, etc), though that could be cool sometimes, depending on how you use it.
If you have examples, I could help point out some things specifically you can improve. Even if it's not theory-related, it's easier to help you if you have concrete things to help with. =P