#1
Hello everyone I'm new to this forum and to guitar and was wondering if some of you nice people could help me out with some questions.

1.) I was wondering how you know how to stay in Key for soloing and chord progressions, are there good sites on the web for advancing myself in that area of playing?

2.) And also any good, preferably straight forward and easy to understand theory books that are out there?

Thanks for taking the time to read my post, thanks in advance to anyone who replies with some help.
#2
To be perfectly honest, I'm quite lakcing in my music theory. I understand it, I just don't apply it. It's easy for me to stay in key when I solo though, because I can hear when I'm playing the right notes and when I'm not, thus I can plan out the finger patterns for staying in that key.
Proud owner of an Engl Thunder 50 Reverb and an Ibanez S470

"The end is extremely fucking nigh..."
#3
For theory books visit your local music shops. Most of the owners would be private musicians/music experts/music tutors themselves. All you have to do is ask them about good music theory books for beginners and they'll show you. For the moment, you could try looking around the internet and UG.
#4
Look around on the main site (ultimate-guitar.com) in the lessons section. There you can find TONS of user-written lessons regarding chords and scales, and most importantly: using them to solo.

If you're really into the idea of classic rock style solo's check out the Pentatonic Scale Shapes . These are incredibly simple, user friendly, and cool-sounding scales that many guitarists use. Don't get me wrong.. just as everything else in music, these scales can serve many purposes and pump out lots of different sounds when used correctly.
Like I said, very user friendly and IMO the best place to start.

If you have more of a jazz vibe (lots of other styles too!) , check out the scales called the Modes. In a very simplified explination, the modes make up a scale-network that covers every note in a key. There are 7 modes, one to match each scale degree in a key.

Anyway, learning these scales and practicing them EVERY DAY will give you a sturdy set up to solo over any chord progression. Over time (its different for everyone) your ear will develop and you're going to be able to hear mistakes, just like Smokey Amp said.
Remember, just like anything else, soloing improves the most by pure experience.

As for the books, I don't have any idea. I've been taking lessons for as long as I can remember, my theory was taught by an instructor.

Search the site, its a goldmine of info