What advice would you give your beginner-self?

Try to find a friend or two who can support your learning.  I’m SO lucky to have my amazing friends here at Tonebase, because the wonderful people I meet at work or the gym simply don’t “get” why I like to spend time repeating sections of a piece over and over. 

Spend a lot of time finding a good teacher that you really like.

You will save time by slowing down so practice slowly and work on the week areas.

Don't stop playing music for years because you do not have a plan and life WILL take over if you do not plan.

Do more sight reading and worry about the actual notes less.

Excellent advice! I would say have measurable, clear goals. Be patient with oneself and find positive attributes to build upon.

My advice would be "play lots of repertoire from the beginning, and the technique will come."

Starting out and mostly self-taught, I spent many years hyper-focused on doing as many technical exercises over and over (Hanon, Schmitt, Philips, Pischna, etc.). I felt that mastering all these technical things would put me on the road to mastery. However, I would play very little actual repertoire - I spent any given practice almost 80-90% on exercises, and what little time remained on some repertoire. Seems boring (and it was!), but for some reason I had convinced myself this was the best way to learn piano. I also think exercises felt like something I could master because they are usually short and easy to memorize as patterns. However, it seemed like I couldn't play real music or even play these techniques in context.

It wasn't until I worked with a teacher who looking at what I practice immediately basically said I need to flip the ratio of technical exercises to repertoire - 10-20% on exercises, and the rest on my time repertoire. Also exercises should be focused on addressing an issue in your playing, not practiced randomly or mindlessly for the sake of it. This felt scary but ever since then, my piano technique has exploded exponentially. I've discovered that many "exercises" can be found hidden in repertoire itself, and you get to enjoy playing real music. If I need to pump up the challenge, the best trick I learned is to take passages of repertoire and simply transpose them. Best of both worlds as you're playing real music, but you also get to apply it to different keys and fingerings for technical exercise, and it helps with ear training too!

Paramount: set reason expectations. Understand the and enjoy the sounds from your "wrong" notes. They are part of the greater pallet available when improvising. I spent way too much time on Hanon and not enough sight reading and almost no time on theory nor improvisation. So I would rebalance making sure I understood theory especially functional relationships, some sight reading and improvisation daily (these should be fun time) and lastly focus deeply and slowly on one "recital" piece. Learn the what and why of the piece, not just how to play the notes. Praise yourself everyday you are at the piano (read Just Being at the Piano by Mildred Chase).

As others have stated: you need a guide for the adventure. Make sure the guide shares your values and expectations.

“No Pain, no gain” is not for piano.  Find a Taubman teacher

I always like to sight-read both hands the entire piece....I would tell myself ok but after the first time through  to go for ' chunks' ,'more difficult passages' first...nobody every really taught me how to practice . But hey, I have a degree in music and I do know how to practice now:)

I regret answering no thanks to an offer my piano teacher suggested, which was to invite his colleague piano pedagogue to listen me playing. I was scared of playing piano in front of audiences. and I didn’t think it was necessary. I had already a teacher who inspires me. I wish I had known better and grabbed the opportunities. 

Piano learning has lots of fun.

Stay calm, be patient, be positive

Practice purposefully (Don't keep playing what you've already mastered).

Invest in a competent piano teacher early on. (You can't teach yourself to play by only using how-to-play-piano books no matter how hard you try) 

Celebrate your hard work and effort, and stop comparing yourself to others (because there will ALWAYS be someone better than you). 

Enjoy the journey (because it's a marathon, not a sprint). 

Be gentle to your piano, so don't hit it, but pet it like it' s your dog (considering you don' t hit your dog).

It will sound better, and it will prevent you from having lots of technical problems.

Don't be afraid to change teachers until you find a teacher that you connect with.