One of the things that has been impressed on me over the years as I’ve grown in my understanding of proper piano technique is the importance of correct bench placement and height. This is often overlooked by pianists, but is essential for producing good tone quality, establishing correct hand position, and avoiding injuries. Here is a helpful page with explanations and pictures demonstrating proper bench height and posture at the piano: Proper Seating at the Piano
Also, here’s a post I wrote several years ago on Gravity, Strength, and Conduction – three areas I emphasize from the very first lesson to help students establish good technique habits.