There is more than one answer to that great question.
1) Take lessons the traditional way. Go to scheduled lessons with a qualified instructor once a week for 30 or 60 minutes.
2) Teach yourself from a “Teach-Yourself-To-Play-Piano” type of piano book which has an accompaniment CD or, in some cases, DVD. Here are a few options from Amazon.
Or for those who prefer the Dummies books. . .
3) Another great option is to utilize the latest technology trend – learn piano online through a system of videos, e-books, and audio clips.
Each one has its unique way of teaching and one size does not fit all.
I think in today’s standards of learning, option #3, learning piano online, is probably the most flexible method of learning.
What’s nice about it is that you can work on how much or little material you want each time you sit down at the piano or keyboard. Only time for one video or one page to read – that’s perfectly fine.
But then there are those days when you might have a little more time and desire to watch and apply more skills (say maybe 3-5 videos, or examples to try), moving your progress forward even further.
The greatest benefit to online methods is the complete flexibility!