I've mentioned this in previous posts, but I feel it needs to be repeated. As a musician if you want to improve start a band!
When I started learning guitar at 13 all I wanted was to be in a band but when you first start out, unless you have a group of musicians starting out with you, it may be necessary to develop your skills alone first. Personally I learned every AC/DC, Metallica and Guns N' Roses song I could in the span of about 2 years before I was good enough to actually be in a band but once that time came it took me 2 months to see a level of improvement that had taken me the full 2 years prior. You don't even necessarily need to start your own band, you could slot right into a band that already exists, but if you can try to join one where everyone else in it is slightly better than you, that will act as your driving force, catching up and keeping up with the other members of the band.
There are several things that being in a band helps you with. Collaboration with other musicians can create both support and friendly competition that helps you boost your skills and your band mates' at an amazing pace. Through this you can boost your abilities in regards to theory knowledge, song-writing skills, stage presence, ability to play through mistakes, how to compensate for other musicians' mistakes, improvisation skills, professionalism, PR and even things not related to music such as emotional intelligence and people skills. If you want to be a musician of any kind start a band, and start that band as early into your musical career as possible!
I began my first band 2 years into my musical journey, and although there was a fair amount of disagreement there was also a sense of being part of something bigger than myself and what I could accomplish alone and this was a big part of what made it all worth it. Through our disagreements we learned how to better ourselves musically and now, although that band ended nearly 10 years ago at this point, we have all taken the lessons from those experiences with us throughout our lives since. It's certainly a huge part of why I am a musician/audio producer. So in conclusion start a band, learn from others, don't be afraid to let yourself be creatively vulnerable with your band mates and take from the experience all you can and bring it with you to the next adventure.
Ross