I've been playin guitar for a few years now, have some knowledge and a decsent player. I have recently got a band together and started doing covers for the first few weeks. Now we want to start writing original material. My question is how do you know what notes/scales/chord progressions to use. I mean, do you use a major scale, or a pentatonic scale and do your chord progressions/ key coincide with this? Bascially, how do you write a song on guitar?