I have, over the years made many dramatic changes to the ways I was taught to practice. In most occasions the changes came about due to external circumstances that had nothing to do with the piano, and which forced me to practice in a different way.
In a few cases they came about because I heard about them (either from other pianists or from reading), I tried them out, found out that they worked better and adopted them.
If I had to select the three most important in terms of their staggering consequences, these would be the ones I would choose:
1. Practice in small segments, sometimes as short as 10 – 15 minutes. I used to practice for hours on end. Yet my playing was completely mediocre in spite of the heavy investment in time. Then, due to some unforeseen events, I was not able to practice for more than a few minutes uninterrupted. So instead of practicing for three-four hours solid, now I was forced to do several 10 –15 minute sessions a day. In the beginning I panicked and fretted. And yet, as the weeks passed, something remarkable happened: not only such small sessions were not having any of the devastating effects I believed they would, as my playing started to improve perceptibly. This was many, many years ago. Since then I have never put more than 30 – 40 minutes of practice (at the piano) in one single session. My playing – rather than suffering – improved enormously. And there are days in which I do not play at all, without any perceivable consequences.
2. Practice the music, not the playing. The obsession with speed, bravura feats of piano athleticism and so on are well known within the forum. However if you let your technique be dictated by the musical requirements of the piece, you will find out (like I did) that the playing improves astonishingly.
3. Do not skip steps, do not look for shortcuts. I really got to grips with this one as a result of teaching. Teaching forces you to go step-by-step over the same piece repeatedly with each student. I started noticing that the pieces I taught were the ones I really excelled at. An honest comparison between these pieces and the ones I was working on by myself showed that I was skipping a lot of steps and cutting a lot of corners on my pieces, while with the ones I was teaching, the teaching situation basically forced me into the proper discipline. Since this realization (many years ago), I have incorporated this into my practice routine, which basically means that after learning a piece, I learn it again from scratch step by step. By the third-fourth learning, the piece is so thoroughly ingrained that even if I stop playing it for a couple of years I can still play it perfectly.