Of course you should have a firm grasp on all the notes on the fretboard. Then I would say start off with scales...Major and Minor then move to others based on what king of music you play. This will lead to solo building as well as finding good chord progressions to match solos and riffs. There are good resources on the web that can teach you some simple theory. I used Cyberfret.com. Theory will help you extremely, all great guitarist know a little theory ;) . Yes even Hendrix