I try not to dwell on things that can’t be changed but if I could tell my teenage self anything about the future, it’d be these things:

• …Move out of your comfort zone.  Comfort zones may seem safe, but ultimately aren’t.  
  For a while I was really lost because of this, and luckily got pushed out of it.  That doesn’t always happen without your own efforts, though.  More recently I heard advice about getting better by progressively becoming a big fish in whatever pond you’re in before moving on.  A few years ago I was trying to swim in a puddle and didn’t even know it, and it almost made me quit drawing.  I almost quit because I didn’t realize I was stuck in a comfort zone.
• It’s a gift to be surrounded by people who are on your level or better.  You’ll grow pretty quickly.
• If a mentor you’ve outgrown gives advice you’ve outgrown, don’t get uppity– they helped you outgrow it.
• Sometimes even people you really respect/admire don’t know what you should do next.  Don’t ignore strong instincts in order to placate someone.
• Don’t be so insecure that you try to simultaneously feature every art skill you have under the sun, in every piece.  You can wreck a lot of work trying to do that.  Do what works for the piece.  Don’t let technique get in the way of what the piece is trying to communicate.
• If someone expresses their fears/insecurities to you in the form of criticism it may not necessarily be helpful, but still take it into consideration.  Really, just don’t be blind to when someone is right.  On the reverse side of that, don’t be blind to when you’re right, either.