Common problem: we adjust our bodies to the instrument. Whether standing or sitting, keep your head balanced above your center of gravity. Bring the instrument to you.
Do the Dippin’ Bird
That little bird bobs up and down but the legs stay in place. Watch this video: I keep my posture balanced over my center of gravity while the trombone moves up and down. I don’t adjust my posture to the instrument.
This can be a very useful exercise.
Ever been hiking? If you needed to drink from a stream, would you choose the moving water or the water that is just sitting there?
(OK, I’m hoping the answer here is pretty obvious).
Long notes are like that. Don’t let them become stagnant. They should always feel as if they are moving somewhere (either building or decaying).
Blow through the end of the note.
Blow into the next note!