We've come up with a list of 12 ways to improve your tone, and thereby your playing ultimately, without buying anything. This isn't a total absolute - end all/be all list but rather of 12 ways that we came up with and that works well for us. Those 12 ways include:
-Use a good tuner
-Practice without headphones
-Stand when you practice instead of sitting
-Practice playing around chords instead of just playing a scale
-Practice your vibrato, and practice it to a metronome or drum track
-Use Karaoke-Version.com to download a multitrack version of a song and remove the guitar to practice with the track
-Practice with a drum loop or metronome
-How to make the best of hitting the "wrong" note in front of the audience
-Listen and learn to other instruments and singers to mimic how they phrase their melodies and note choice
-Take a break
-Slow down the tempo of a solo to learn it note by note and each nuance
-Learn chords everywhere on the neck, as well as the scales around those chords (See CAGED system)
Comment below with YOUR favorite tips!