Watch the 100+ C Major Scales online guitar lesson by Frank Vignola from Modern Method for Guitar
The reason most guitar players can't play what they hear is because they haven't mastered the fret board. The guitar is the only instrument with so many options to play a simple C scale; and also why it is so hard to sight-read on guitar. Begin working through my 110 Essential Fingerings for a C scale. Learn 2 fingerings per week and your knowledge of the fret board will increase tremendously in the first few months. This is the key to connecting your fingers and your brain to your ears and playing what you hear. Do not concern yourself with memorizing all of the variations. The point is to understand how you can make small changes to the fingerings to come up with many variations.