I took music theory with my percussion teacher at school. I loved it. Since I had already been playing percussion pretty well for 7 years, learning theory was just a "Oh wow so that's how it works" thing. It made me love music even more because everything just makes sense. There were so many rules, and when you know them, you know how to bend them to get what you are looking for. It became all about pushing the boundries. I still barely scratched the surface since a lot of the kids were kinda behind me. The percussion director worked theory into a lot of what we did, so I already knew some of it, but by the end of the year, there wasn't anyone in my percussion class who knew more than I did, even the kids who had taken theory the year before. I'd research it after school and stuff.
It is true a majority of famous musicians don't know how to read music, but having the ability opens so many more doors for you as a guitarist. (or drummer) After all someone makes the music you hear in every tv show/movie/commercial you see. Those people were called up and learned it in minutes. You can also play in things like broadway and orchestras or symphonies. So if it's something you'd like to make some cash with, theory and stuff is the way to go, or at least some understanding of sheet music.
Anyway to answer your question on progress, (for me it was drums and percussion) the first little bit is the hardest. I'd say find as many different kinds of workouts you can. (like warm ups and exercises) and work on them really slow and really fast. Metronomes are also a really good idea, but messing around is one of the best ways to learn what works and what doesn't. Like I said, I had been playing seven years before I knew the why behind anything.
Like Treb said, listening to music helps too. Once you know what your doing, when you hear a guitar part your brain starts figuring out how to do it on sound alone, before long, you can hear a song and play it after just a short time of trying to find the notes. Of course the key to getting good at any instrument is to keep playing it as much as possible. Also find a teacher that is interesting to you to learn from. I think part of why I love it so much is because the teacher I had was very cool. He was extremely laid back and to the point. It was like "Dude, check this out, isn't it wild? Look at the patterns the notes make" Like the circle of fifths, it blew my mind that the intervals worked the way they did. Then I was taught to build minors, and the 3 kinds, then blues. Then we sat back and learned technical names for time signatures and stuff, and different terms for moving notes, then all the modes of scales. We were scratching the surface of progressions when the school year ended. We also used a program called sybelius to write music, a program I hope to own soon. I'd recommend getting it or a program similar, then you can write things, hear how they sound, and learn to play them on your own.
I guess the biggest thing I noticed in my own playing was that I'd always hit a "speed wall" it was a level that I would just max out at and couldn't get any faster, but once I worked at it and got passed it, my ability skyrocketed over the next couple months. I don't know if that's normal (since no other kid said anything about it in class) but it helped me a lot. I'm currently hitting my 3rd speed wall. 16ths at 180 beats per minute. I'd hit that wall for other things too. There's be a place that I didn't think I could go any further with notes on the staff or being able to hear stuff (ear training) and even scales. I always worked on it, knowing there was a higher level to reach, and I suppose that's what kept me going. Just remember, the better you know the basics, the easier and more fun the more advanced stuff will be.
I'm on muscle relaxers right now so I may be rambling. My advice in short: play a lot, learn what you can, expose yourself to every kind of music, and get really good at the basics. Good luck!
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