yes, LONG TONES LONG TONES LONG TONES,
every time you practice alto or sop, start with going up and down the full range of notes holding each for as long as you can focusing on maintaining a steady note, not too much waviness. do this on both alto and soprano, this might take between half an hour and an hour and for me it started to show results within a week, my lips were bleeding by then but everything played and sounded so much better.
you might want to look into mouthpieces aswell if you havent already.
every time you practice alto or sop, start with going up and down the full range of notes holding each for as long as you can focusing on maintaining a steady note, not too much waviness. do this on both alto and soprano, this might take between half an hour and an hour and for me it started to show results within a week, my lips were bleeding by then but everything played and sounded so much better.
you might want to look into mouthpieces aswell if you havent already.