Theory 101

Well, first off I am not the most knowledgeable person when it comes to theory but I would say the first three things you should know (in order of importance) are:

1. The name of [U]every[/U] note on the fretboard, theory is useless without knowing exactly what you are playing.

2.Intervals, simply the distance between two notes.

3.Chord theory, this will explain how chords are made, which helps in deciding which scale(s) to use when soloing.

i would definitly agree with what Inr said, but remeber when u practice intervalls and and such you should try to also develope your ear. eg when someone plays an intervall and see if u can recognise it.or just sit with your guitar, learn the intervall shapes, pick an easy one to start with, say a fith, try to sing ot then play it to see if you are correct.

with learnin the notes on the fretboard, i didnt do this but it makes the theory i have learnt very hard to implement.

if you want to know about modes which is related to chord theory, look at the modess and such post, i wrote a pretty long explanation, its my third post.

anyway hope you find it usefull.

Yeah, Inr had a fairly good suggestion. Personally, though, I'd work on scales before chord theory since chords are made from scales. Get all of the Major scales down and you'll have a better start than most.

To add to what Fret spider said about singing intervals,
I read an article by Satch that said to start out playing and singing one note at the same time and then try to sing it then play it, from there try playing one note and singing an interval against it, ie. play an open "A" note and try to sing a fifth "E" up or down from it.

Check out my Beginner to Advanced Series at my lesson site: http://lessons.mikedodge.com

The Intervals and Chord Constuction lessons should give you the fundamentals you need to persue deeper into Music Theory.

After a god understanding of those topics the next step would be Diatonic Theory.