As Superhuman said, you can whack any label on it you want, or try to pin down criteria for it, but progressive musicianship is really just thinking outside the box, and combining different styles in a way that is intellectually and emotionally challenging (yeah, you can feel a prog-head rant coming, can't you? :p ). IMHO the best thing for you to do at this stage is just to get as many techniques, tricks and songwriting skills into your musical toolbox as possible. Investigate a variety of different styles of guitar playing - rock, folk, pop, funk, jazz, classical/neoclassical, metal, reggae, whatever interests you plus a bit extra to broaden your scope; and pick up as many different techniques, especially rhythm and chordal techniques, as you can. Listen to plenty of progressive and art rock; listen to how the greats like Pink Floyd, Jethro Tull, King Crimson, Frank Zappa, Yes, Van der Graaf Generator, the Moody Blues, Opeth, the Mars Volta, Dream Theatre, Supertramp, Rush, the Sonic Youth and others combine various musical influences. When putting your own material together, don't cut-and-paste from the greats; think about how YOU want YOUR music to sound, and take note of how the greats synthesise their influences in putting it together. Remember that prog music is not necessarily just shred soloing over odd-time chord progressions in weird tunings (although by all means it can be if it's outside the box and stimulating) - it's whatever you want it to be. So the main thing to do is to add as many styles as possible to your guitar-playing palette, and the progressive-ness ought to eventually come out through your playing and songwriting.

Sorry, that was a bit of a ramble :o