What advice would you give your beginner-self?

Actually DO what I’ve been told so often to do: practice in segments, rather than “playing” the whole piece over and over. Get every part up to the same level, instead of stumbling through the hard bits.

It is so tempting to enjoy playing the piece, but if 10% or 20% of it always presents stumbles, get those fixed! Repetition, repetition, thoughtful and focused repetition! 

I would get the best teacher I possibly could, who also taught theory in conjunction to the music being learned.

To recognize that piano is hard to do well and to be patient with consistent progress. 

Subscribe to Apple Classical which is such an extraordinary archive of great performances. If you’re having trouble finding exemplars of common student repertoire, this is useful: 

https://www.deutschegrammophon.com/en/catalogue/products/piano-lessons-christoph-eschenbach-12196

Do not try to teach yourself. As others have said, find a good teacher and:

1. Show up

2. Work hard

3. Listen to what your teacher says and act on their advice

I would say to myself, spend more time sight reading and ear training.

My best advice to my former self: Listen to your teachers! Seriously, listen to your teachers!

Get a teacher who is trained as a teacher; one who chose that as a career, not a performer who either needs the money, or is suitable for training other current or would-be professional performers in a master class.  

One of my teachers was trained at a prestigious European institute and said that she as a performer was encouraged to look down at the mere teachers.  She teaches interpretation very well, as you might expect, but admits she has no pedagogical system she works with.

I now have a teacher who has chosen teaching as a career and spent years learning how to teach.  The difference is profound.  

Hi. I'm a beginner myself so in a few (or maybe a lot of) years my answer could be more complete... but... so far I can say I started from zero in 2020 when I was 30, not even knowing which keys corresponded to C..D... etc, but I started in a "commercial school" for kids and pretty soon felt like it was really easy going and not at all what I was hoping for, since I really want to learn classical music, so I left and tried another teacher from another school of that same genre, and even though the teacher was a bit more serious, it still felt a bit far from what I was looking for, so I left that too and after a while I decided to search for a real piano teacher and performer. I am currently beeing taught by a conservatory piano teacher, it's been only 4 months so far, but the difference is huge and it has been amazing so far. So my first advice would be to start right away with a very good piano teacher with a professional background in teaching real pianists. The second would be, if you can, get a real acoustic piano. I've used a digital yamaha P-45 (the first teacher recommended) and I didn't feel like spending too much money on something that I wasn't sure would last for me... and only a month ago, with the advice of my new teacher, went for an upright acoustic, since my house doesn't really have room for more, and I feel the difference in everything, digital is very practical but it doesn't give you the pleasure and feedback of a real piano and that will not only help you improve but  for me, it keeps me much more engaged, I can't be away from it for too long. Another thing I've been discovering is that piano playing, if you really want to do it right, is MUCH MORE complex than I thought... but I really knew nothing about it. It makes me feel a bit scared of what I'm getting into, starting so late... but I'm loving the challenge. It is very frustrating and I have to learn to be very patient with myself and understand that this is going to take a lot of time and dedication before I feel like I can really play something that sounds nice coming from my hands. But I know now that I have an amazing teacher that will help me in that process and that is fundamental! 

As others mentioned, teachers is really important.  

I'll add to that to get multiple teachers as one develops (or felt stuck), at least a lesson or two (eg. masterclasses).   It's important to get feedback from other musicians as early as possible.  Everyone teachers (and students) has areas of strengths and areas they overlook.

Do more technical exercises in a fun musical way.  

   -Czernies are nice for the ears. Even hanon can be practice in a fun way.

two more:

RYTHM 

   - Develop this skill independently from the pitch.

Learn to LISTEN!!!

   - Not just for the pitch, tone COLOR, breathing etc.

Find a great teacher who can teach each concept step by step.