Chord progressions are kinda hard to master, but once you do so you'll be glad you did. A chord progression is a pattern of chords that is repeated throughout a song. The most widely used level of repetition is at the verse level, i.e. each verse uses the same chord progression. That's simple, effective, and provides coherency that links verses together as part of the same song. Of course, your chord progression can repeat on a much smaller scale. Two of my most popular songs, Electric Clay and the duet Nothing, consist of a simple 4-chord progression that is repeated 4 times to make each verse. Very, very simple, but people are always asking me to play those songs. It's things like that that make me believe in my 'golden rule' of composing: Simplest is bestest.
What chords sound good? Well, here's a few ideas:
In a major key:
I: The root. Start and end on this chord, unless you know what you're doing.
ii: The 2 of a major scale is minor. Be careful using this one. Sounds best in a ii-V-I cadence.
iii: The 3 of a major scale is minor. Again, be careful using it.
IV: The major 4 is a good chord to use. Along with I and V7, it supported several eras of music. :)
V: Yippie! We all love the major 5. Stick a minor 7th on it and you get V7, a very popular chord. This is the 'best' cadencial chord.
vi: The 6 of a major scale is minor. In certain circumstances, this sounds good. This is the 'relative minor' of the major key.
viio: The 7 of a major scale is diminished. Be very careful using this, and use it only if you're sure you want it. Can be used as a substitute for ii.
In a minor key:
i: The root. Start and end on this chord, unless you know what you're doing.
iio: The 2 of a minor scale is diminished. Generally avoid it.
III+: The 3 of a minor scale is augmented. Not so good. Lose the #5 and you get the 'relative major' of the minor key.
iv: The minor 4 is a pretty good chord to use, most of the time.
V: The 5 of a minor scale is major. You might think that's not what you want, if you're going for a minor feel, but the contrast provided by this major chord is a good thing.
VI: The 6 of a minor scale is major. A pretty good chord to use
viio: The 7 of a major scale is diminished. Not so good. :/
Of course, if you follow only those guidelines, you end up using only 4 or 5 chords. This means that you're going to run out of new song ideas pretty quickly. And your songs won't be terribly interesting either, unless you have really good melodies, or really interesting rhythms, or hips that shake in suggestive ways, or any of the other things that allowed blues and old-school rock'n'roll to survive for so long. Most songs from those genres follow a simple 12-bar chord progression:
I_ _ _ _
IV_ _ I_ _
V7_ _I_ V7_
That's the major 1 chord for four bars, the major 4 chord for two bars, back to 1 for two bars, up to the V7 chord for two bars, then one bar of 1 and one of V7. Then you repeat the whole thing, for as many verses as you want.
That's called the Basic Blues progression. The key a particular song is in doesn't matter when trying to figure out a chod progression, only the relationships between the chords does. Although songs such as Roll Over Beethoven, Twist and Shout, and Hound Dog are in different keys and have different rhythms and melodies, the underlying chord progression is the same.
If you don't understand all the numbers I used when I was talking about what chords work well, poke around in Chord Helper in CLTH for a while. You'll figure it out after a little while. And if you don't, come talk to me (or send an e-mail to CoriakinCL@gmail.com), and I'll try to answer any questions you have.