Listen to as much music as you can. Think about the music and analyse it. Keep an open mind to all genres of music; they all provide a useful learning opportunity.
Analyse all the instruments you hear, not just guitars. Listen to how they fit together. Music is about emotion, so don't get bogged down in theory and technical ability. Otherwise you will be boring and unoriginal.
Theory is not essential but can help you add direction to a piece of music. It can give you ideas when it comes to adding a chord, solo or riff to a piece of music you are working on.
Lefties can reverse scale/chord diagrams with certain computer software, making them easier to read.
Playing an open string can be used to give your fretting hand time to move to other parts of the fretboard. Open strings also allow you to experiment with different sounds. Try letting an open string ring and harmonising over the top.
Tapping or slide guitar can give rise to string noise and unwanted buzzing sounds. To reduce this try tying something just below the nut to dampen the strings (shoestring or fabric). Alternatively attach a toothpick under the strings just behind the nut.