Things to Avoid:
1. Forcing the student to play along with you
2. Not allowing the student to play any way except for a certain way
3.Using opinionated and exaggerated language in a lesson when teaching.
4. Making the student play Chopin and Liszt with the metronome (unless they are someone like Lang Lang
)
5. Giving them atonal/not-very-tonal pieces way too early (I. e. No Prokofiev, Bach Fugues, Schostakovich, Bartok, or Copland until they've reached the stage where they appreciate the beauty of those works)
6. Forcing them to attend student recitals
7. Talking way too quiet
8. Having an extremely dry piano
9. Having an uneven piano
10. Exaggerating while you copy the student (unless the student is exceptionally stupid and cannot figure out what they are doing weirdly unless you exaggerate)
11. Telling the student that they are not ready for certain pieces (unless they want to jump from Fur Elise to La Campanella
As a piano teacher for 20 years now I disagree with many things listed here as being something to avoid 1,2,3,4,5,6,8,9,10,11
"Forcing" doesn't necessarily to me mean mindlessly telling them to do it and try again and again but to give the student various tools to achieve it. They should accompany the teacher when learning a piece and play in time, you don't always have to do it but it comes up often as good practice especially when exploring new pieces.
Some early beginners require direct instruction as to what not to do and constantly reminded to avoid certain movements (eg dropping wrist below the keys) yes many issues in technique is formed over time and one should not simply try to copy/paste deals of mastery but often issues need direct correctives rather than long term manipulation.
Using exaggerations are good to clearly highlight an issue it depends on your personal style but none of my students mind when I over exaggerate their errors and rather appreciate getting a clearer view.
Metronome use in my lessons are for small sections only so all students should know how to use it, you wouldn't make them play an entire piece with one though that seems unuseful.
I let students explore what interests them, there is no set path, but to develop as a pianist there are thousands of pieces to go through, to simply think you must do this book completely or another is mindless, to be a complete pianist you need experience in many regions and there is no problem expanding ones listening/playing experience to styles they might know little about. As a teacher I must know the many levels building up in the thousands and thousands of pieces that is available for the student, then I can move my students through the levels and ensure they have the experience to draw from to efficiently learn their music, poor teachers give their students pieces which take a lot of time to learn, it should be fast paced with new pieces learned at a good rate, not a slow output with difficult pieces.
Attending performances makes students feel less isolated as the only person playing the piano. Encouraging them to attend performances of their peers or professional concerts is beneficial, especially for those who always compare themselves with others, they must learn not to do it and exposing themselves to performances is a good way to desensitise especially with some good talking to beforehand and after.
Certainly I will tell a student if something is too hard, it is never that they can't play it but I remind them they simply will waste time labouring on their difficulties, some are pig headed and will not change studying pieces they love you can't blame them, but proper study requires efficient learning, it is such a shame watching students of music waste months and months even years with single pieces where they could be learning so many easier pieces and develop their learning craft to a higher level.