One of my favorite things to do on guitar is improvise along with another guitar... (who doesn't?)  But one of the first problems that I encountered initially in doing lead guitar was that I didn't know what notes sounded good with what chords and I didn't know how to find them, so I would just stumble around the fretboard, hoping the next note I hit would sound good.  So in this lesson I hope I can save you from the lack of knowledge I went through by teaching you the notes on a fretboard and how they work with rhythm guitar.  Let's begin, shall we?

Here is a map of all the notes on you're guitar neck... it's basically a key to everything on this lesson so study it carefully.  (by the way it's an illustration of your guitar neck if your gig-fiddle stood up and looked at you.  It's in standard tuning.)  Here is goes.
 

You could use this chart to find out the the G chord (320033) uses the notes GBDGDG and you could pick those notes anywhere they show up on the diagram and be in key.  Also, in the key of G are the chords, C, D and Em.  C (x32010) would have the notes CEGC and E.  Em (022000) has EBEGBE and D (xx0232) includes DAD and F#.  That means that the notes in the key of G would be B,C,D,E,F# and G.  So the in the key of G the essential "hot spots" are as follows.