Little things you might not have thought of can make a big difference in your playing.
Always Keep Your Guitar Handy
You are far more likely to pick your guitar up and play if it is already accessible. For some reason, whether it's laziness or just subconscious, you are less likely to go or even just open your case and get your guitar. Purchase a simple guitar stand and leave it out. Even though this is not a very technical tip, the truth is, the more you play, the better you will be.
Less Is More
Try not to always reach for your effects board or various peddles. When you restrain yourself from options, your are forced to be more creative. Many times, not even plugging into your amp is beneficial because you cannot rely on distortion and reverb to cover your mistakes. Therefore, playing in as a clean a setting as possible, such as unplugged, will bring to light many mistakes you might be making but would not notice otherwise.
Step Outside Your Comfort Zone
Many guitarists deprive themselves of being better because they do not want to play different styles that they are not accustomed to. Even if it is a genre or type of playing that you don't necessarily like, it is very important that you experiment with various forms in order to be well versed in your craft. The more you know the better you are and it is always helpful to add different techniques to your playing.
Jam More Often
Without a doubt, playing with other people is a guaranteed way to grow in your skill. When you play with other guitarists, not only do you get to bounce ideas off each other, you'll find that you are actually pushing yourself and your playing harder to keep up.
Never Stop Learning
You are never too old or too good to learn more. Whether it's by teaching yourself or deciding to take lessons, you need to progress or you will plateau. Buy a video, buy a music theory book, or look for lessons online. Just remember, however good you are, there is always somebody better out there that you can learn from.