Nowadays for a lasting major career? Geez...
Talent, discipline, luck, strong nerves, good general health, financial support, mental and physical stamina, dedication, strong memory, proper guidance, focus, technique, musicianship, appealing stage manner, playing refinement, connections...winning a major competition doesn't hurt either...critics who like you, a succesful debut CD, a good manager, a good label...did I mention luck?
Am I leaving anything out? So few can actually pull it off for any length of time...
If a highly-talented young person were getting started, I would recommend getting a quality CD together, for promo purposes and distribution, a quality picture, make a website for yourself with pictures and audio samples and forward it to anyone and everyone, explore some lesser-known repertoire in addition to the popular standards, try the competition circuit (for the experience if nothing else), and try to make useful friends, including other musicians(not just pianists), recording engineers, video people, people that work in piano showrooms and halls, etc.
STAY AWAY from "sponsors" and "supporters" who basically want alot of time from you, and talk more than they put up (usually older people with money - they are vampires) - if they don't cut a check immediately after the first lunch or dinner with them, LOSE THEM! They will waste your time - don't waste any time and energy on this type, who claims to know this one and that one, etc. and promises to introduce you to the cousin of so-and-so, and all you have to do is hang around them and kiss their ass for a few weeks - they will never deliver anything worthwhile! Remember this - it will save you some disappointment later...
Play anywhere and everywhere for free in the beginning - don't worry about fees, just get out there and meet people and get the experience...you can be more mercinary later on...
Don't get involved with managers - hang in there by yourself for a while - make your own moves and be your own agent - sell your CD's at your concerts, promote your website...
Work an interesting repertoire angle - maybe Clementi, or Busoni, or champion some lesser known composer - there's always time for Chopin Ballades later...
OK - I'm tired - going to bed now - hope this helps!
Good Luck!