Here's an email I recently sent to a friend who is also learning guitar:
I’d like to share a few things that I found helpful in my guitar journey, understanding that I don’t claim to be a fantastic guitarist and knowing that you likely know most, if not all of what I am about to share.

I think many guitar players learn chords and barre chords, and perhaps venture a little into lead guitar while believing that they have learned most of what they need to know. I thought the same way for a long time. I discovered that chords and barre chords were more like 60% or less of what a well rounded guitarist needs to know. The other stuff I picked up on, which I strongly recommend, is the following:

1. There is a whole world to be discovered on the high E, B and G strings of a guitar. There are some shapes that can be played down there, that would be very familiar, that can be useful in the following ways:

a) as another way of playing chords, that emphasizes the higher sounding end.
b) typically used in funk, disco and modern music to produce some pretty nifty progressions/sounds.
c) sonically, as an alternative to playing a full chord, whose lower end, will sometimes collide- compete sonically, with a bass guitar. This is particularly important in recording music where you want to carve out frequencies positionally within the sonic landscape. Where sonic overlaps and collisions occur, it muddies the clarity of certain instruments. Thus, using the higher register as an alternative, with a bass guitar looking after the lower foundation, is often a good mix. Again, more important in recording although there are also benefits in playing live.

2. The Penatatonic scale, and it’s various positions along the neck is probably the biggest bang for your time spent, in terms of its immediate usefulness in blues and rock. Once the various positions of the pentatonic are learned, it can easily be applied to blues music or rock. A neat little trick occurs when you move the position 3 frets back. When doing so, you switch from a bluesy sounding solo, to a happy sounding solo simply by moving the position back three frets, while remaining in key.

3. Learning the modes is also a very good investment. It is initially a mind twister as it runs somewhat contrary to other approaches to learning other aspects of the guitar. But once the concept and payload of modes clicks, it is well worth it. If you have not used modes and wish to revisit them, I strongly suggest you learn all the positions of the major scale (also known as the Ionian mode). Once that is learned and one is fluid with it, it can be used to play virtually any other mode. The beauty of it, is that you can easily solo to almost any genre including music by AC/DC (typically mixolydian), Santana (often times Dorian) and the like.

I hope some of this is helpful. Again, I am no virtuoso and I had to give up playing for some time due to my health. But these are some of the things I learned in an effort to try to improve the breadth of my playing.