Never - "Avoid"
I can't! All my sheet music is Urtext (original versions), with all the ornaments that the composers could cram into the music that was initially composed for the harpsichord where keys are lighter and so ornaments are easier to play.
"Trills: My teacher says practise slow and count them. Use wrist movements to help mark time. I say just go for it."
I don't know what "wrist movements" mean in this context but your teacher is correct for the rest of it
On the harpsichord you just move your fingers for the trills. I guess that's the kind of mechanical advice I need for the piano, because doing trills and other ornaments just by the force of my fingers gets quite painful after a while, all the way up to my elbow at times.
Can you try to explain those "wrist movements" to me?
"The shorter ones: think a sudden burst of energy, but be careful where you want the stress to be"
Oh they have to be a lot more precise than that to please my harpsichord teacher
All those different ornaments mean different notes played in a certain sequence.
I know how to play them each, but I think I need some pointers for the "biomechanics" of playing them on the piano because the harpsichord way is going to give me tendonitis soon.