I seriously need to learn to have a better ear for music. I think I have a good sense of melody, but I suck when it comes to notes and pitches. What is the fastest, most effective way for me to develop relative pitch?
The fastest way certainly isn't the most effective. What you need is ear training and patience, try learning to play songs by ear and you will see that you get better along the way.
Have your guitar tuned properly all the time and listen to the sounds of open chords. You'd be surprised at how well one's brain can pick out familiar notes when you put them in context (mentally). I.e. a C has notes ordered in a distinct fashion when compared to an A...envisioning the open chord really helps me.
I don't know if you're doing anything with theory besides guitar but I am taking music theory this semester, so excited, and its really intense, as in we are expected to get all of those sorts of ideas and implementing them. What has helped me the most was sight singing, in particular the fixed-do method. I'm still learning the fixed-do solfege but its helping a lot. Other things are learning to sing intervals and sitting at a piano singing an interval and playing it to check yourself, not doing it the other way around. This will help with hearing intervals which is half of the battle.
Stock Gibson Pickups from a 2005 V, I think they're a 498T and 500T set FS/FT
Duncan Distortion (regular spaced) FS

Looking for: an acoustic, recording gear, or $
Last edited by FFFDFEFRFKFFF at Nov 3, 2008,
Take a solfege course.
It's been tried and tested over a few centuries.
Realistically, you ought to expect to keep at it for a couple of years.
Solfège would be a good idea. Sight singing turned out to be easier than I though when I first started.
Something that helped me was to associate a song with each interval. Some of these songs might be a little out-dated for you younger players. So you might have to ask your parents. I'll do these in order of distance from the root.
minor 2nd - Theme to Jaws
Major 2nd - the Major scale song; do,re,mi,fa,so,la,ti,do
minor 3rd - Brahms' lullaby
Major 3rd - For he's a jolly good fellow
Perfect 4th - Here comes the bride
Tritone - Maria (from West Side Story)
Perfect 5th - Twinkle twinkle little star
minor 6th - The theme from Love Story
Major 6th - It came upon a midnight clear
minor 7th - Theme from the original Star Trek (you know, Cpt. Kirk)
Major 7th - The 2nd half of the theme from the Superman movies (Christopher Reeves)
Octave - Somewhere over the Rainbow

I know alot of these song examples are cheesy, but for the most part they're instantly recognizable.
Oh and one other thing, PRACTICE,PRACTICE,PRACTICE.