Now, let's get started.
There are a plethora of artists out there who get by with the same chord progression again and again and again. G, C, D, rinse, lather, repeat, over and over, they practically beat us to death with those 3 little chords. Their problem is they lack the theoretical knowledge to embellish that progression, and as a result, their material can end up being bland and unoriginal.
So to start, we should figure out why G, C, D works so well, and is so effective. And to do that, we'll work backwards, starting with the D chord.
The D chord is what's called the "Dominant," and it has a very special place in tonal music. The Dominant chord is the chord that is built off the fifth scale degree of the major scale. That's a lot of words to describe a pretty simple thing. Starting at G, count the notes to D. G, A, B, C, D. That's five notes, which makes D the fifth scale degree.
You'll notice that if you play a D chord to a G chord, you'll feel a sense of resolution. G will feel like "Home" and D will feel like it needs to go to that G chord. The reason for this is not important right now, all that matters is that it happens.
So before the D chord, we have the C chord, which also has a special name. The C chord is called the "Subdominant" chord, and is built off the 4th scale degree of the major scale. Again, count your notes, G, A, B, C. Four notes, fourth scale degree. The names make sense on this one. The subdominant goes to the dominant, just as the name suggests, and then the dominant, D, goes to G, which is also called the tonic, because it is the TONal center of the progression. We always resolve back to G. Tonic is built on the first scale degree of the major scale, and it's always the chord in the name of the scale. I.e in A Major, A is tonic, and in E Major, E is tonic. In Bb major, Bb is tonic and in F# major, F# is tonic. Never changes.
At this point, I'll stop referring to the chords by their note names and start using a different notation, one that is universally accepted in the music theory world. Instead of note names, I will use the Roman Numerals corresponding with the scale degree the chord is built on.
For example, G is built on the 1st scale degree, so it will be I.
C is built on the 4th scale degree, so it gets called IV.
And D is built on the 5th scale degree, so it gets called V.
Put 'em together, and you get I-IV-V-I, the easiest and most basic of all chord progressions, and the one you hear when you hear that famous G-C-D-G progression.
Now to start adding and changing things. For our purposes, the chords will always stay in the same order, i.e IV will always come before V, and I will always be on either side of those guys. To start, we'll just add some chords in between them to spice things up. And our first dash of spice comes in the form of a minor chord. If you'll notice, all the chords in the I-IV-V-I are major, which is kinda vanilla and bland. Adding a minor chord changes the listener's ear, and really enforces the strong resolution to tonic.
Our first progression will look like this. I-IV-V-vi-V-I. in note names (in the key of G), you get G, C, D, em, D, G. Again, I wanna stress that this will work in any key, and just to prove it, let's transpose it to E major. Again, we have I-IV-V-vi-V-I, however, instead of I being G, now it is E. So we get E, A, B, c#m, B, E. Notice that after the vi chord, there's another V chord. The reason for this is simple. I is almost ALWAYS preceded by V. It just sounds better that way. You can experiment if you like to try things for yourself. Try playing the progression through without that last V chord. You'll notice that it doesn't have that same satisfying resolution that the first progression had.
Our next progression will keep the vi chord and add another minor chord, the ii chord. It looks like this. I-ii-IV-V-vi-IV-V-I. This progression is a longer progression, and in note names, it looks like this. G, am, C, D, em, C, D, G. Notice the addition of another IV chord after the vi. This chord isn't absolutely necessary, but it works well to balance out the progression. An 8 chord progression fits much more neatly than a 7 bar one, but you can continue to experiment without that chord to find something that works for you. Again, this can be transposed to any key you like, let's try F for this one. It'd look like this. F, gm, Bb, C, dm, Bb, C, F.
Okay, so far we've added two chords, ii and vi. Lets look real quick at a couple other progressions using these chords.
Looking at these, we can draw a couple conclusions. The first, and most useful, is that ii always comes right around IV. The reason for this is because ii and IV have the same FUNCTION. ii and IV both serve as predominant chords, which simply mean they both nicely set up the dominant chord. This means that ii and IV are interchangeable, and that you can use either of them, or both of them, to set up the dominant.
The second conclusion we can draw is that the vi chord is always sandwiched between two V chords. There's a reason for this too. The vi chord serves no tonal purpose other than embellishment. This means that it can't work as a substitution for any chord. The main reason to use the vi is to frustrate your listener. After hearing the V chord, the listener expects to hear a I chord, to get that sense of resolution. The vi contains two of the same notes as the I chord, which makes is ALMOST good enough to be tonic, but not quite. It works well to prolong your progression by a few bars.
Another really easy way to spice up your progression is by adding a seventh to your V chord. The D chord contains the notes D, F#, and A. To make it the D7 chord, all we do is add a C, making it D, F#, A, C. That seventh will really make the V chord pull to the I chord, and really make your resolution strong. It works well at the very end of your song, or if you really want a resolution to pop. Don't overuse this guy though, because the more times you use it the less effective it is on your audience.
Yet another little "cheat" to spice up your V chord is to pull this little embellishing number: V-Vsus4-V. This is very easy in the key of G; all you do is add your pinky on the third fret of your high E string, and then take it off again. The end, clean simple, easy, but very effective.
Here's a little table to help you remember the functions of all the chords you can build off the various scale degrees of the major scale.
Firstly- in order. I, ii, iii, IV, V, vi, vii0, I. (The 0 after the vii means that it is a diminished chord. In lead-sheet notation, which is commonly used in guitar tabs, it'd be (NoteName)dim i.e Bdim, C#dim, F#dim.) Notice that I, IV, and V are major, ii, iii, and vi are minor. vii0 is the only diminished chord in the key.
Tonic- I (I is the only chord that can be considered tonic)
Predominant- ii, IV
Dominant, V, V7, vii0 (The vii0 chord is very rarely used, and does not create as strong of a resolution as the V chord or the V7 chord.)
Embellishing- iii, vi (These chords serve no tonal purpose, and only work to embellish the chords around them. The vi chord is much more common than the iii chord, but we'll look a little bit at the iii in a future lesson.)
Phewph! Lots of information. Hopefully this'll help start you off, and keep you away from that I-IV-V-I rut. Good luck!