It all starts with the ears, not the hands. The best way for any musician, green or otherwise, to progress is to listen to a wider variety of music. If you only listen to 12-bar, I-IV-V music, that's all you'll be familiar with, and consequently that's all you'll feel comfortable playing. But if you listen to other stuff, it will start to make sense to your ears. And the distance from your ears to your fingers is short.

Seek out some music that's outside of your usual comfort zone, listen to it for a while, play along with it if it's in recorded form (staunch Mudcat purists aside, most of us do a lot of listening to recorded music). Some musics are more firmly rooted in the I-IV-V pattern than others. So if you're getting too much I-IV-V from your Delta blues, Woody guthrie folk, Appalacian string bands, or British Isles jigs and reels, try something based in modal Elizabethan music, or West African roots-of-blues stuff, or creative fingerstyle guitar (Martin Simpson, Pierre Bensusan, John Renbourne, etc.), jazz from just about any country or era, or anything else you can find. Hell, you might even try dipping your toes into the poisoned waters of the singer/songwriter stream (Mudcatters, please don't hurt me!); you just might find something worthwhile. There is more accessible music out there now than there ever has been. If you open yourself to it, it WILL come out in your playing.