Watch the Dynamics & Phrasing online guitar lesson by Steve Vai from Alien Guitar Secrets: Passion & Warfare
One other thing that I'd like to mention to keep on your radar is dynamics and phrasing. They are so vital in your musical statement. It's sort of like the human voice - when you're talking to somebody, or listening, in order to retain in interest in what they're saying, their intention has to be clear. The way their intention comes through is in the way they're structuring their sentence. It's where they're putting their accents, commas, and periods. A musical statement is similar. Phrasing is like a comma or a period, dynamics are like the articulation, and when they are put into a musical sentence it makes it sound interesting and adds a tremendous dimension. Some people play guitar like they are speaking in monotone, which is fine if that's what you like, but I'd encourage you to exaggerate your dynamics. You'd be surprised how powerful of a musical statement that will make.
Dynamics is just as simple as how hard you hit a note. I would recommend sitting for an hour and play absolutely as lightly and delicately as you can play, transitioning into how hard you can play. Keep going on and on, experimenting with different versions of dynamics and phrasing, and you'll find that these things are very powerful in getting your point across. Many times I see young, incredibly accomplished "shred" type players who I'd like to see take dynamics and phrasing to a whole new level. I'd like to see them take their melodic ideas to fearless dimensions, finding the music that's really exciting and doesn't sound like anything else. No question that it's there, it's just how much can you open yourself up to it. How much can you listen to your own inner ear?