What's one thing you can do TODAY to improve your guitar playing?

Focusing on one thing at a time.

Sometimes learning to play guitar is really overwhelming. There are chords, notes, scales, arpeggios, theory, the circle of fifths, and the list goes on. A common beginner problem is trying to do too many different things and once and becoming overloaded with information. I've got students who surf the internet for info, then wonder how they're going to learn all that stuff. Playing guitar is a time art, it's not something that you learn in a short period of time. Finding a guitar teacher to help you sort things out is a good first step.

Finding the one thing to focus on.

Be honest with yourself, and assess your skills so far. There's no need to learn barre chords if you can't play simple open position chords, there's no sense in learning theory until you have a basic understanding of music, you get the idea. Deciding what type of music you want to play will be the easiest indicator of what you should focus on first. If you want to play the guitar and sing, practice chords. Don't buy a chord book and try to memorize 100 different chords, get a song with 3 or 4 chords and learn to play it at the correct speed, with no time lost between chord changes. Too many times a beginning guitar student will proclaim a song finished when it still needs lots of work. Do you want to play lead guitar? Start out with one basic scale pattern and explore it. Play a simple pentatonic scale and try out different note combinations. Once you know where the notes are, try to play something that sounds musical.

The main thing is to be advancing your playing and moving forward.