I got all of my students back into shape with long tones and slurs. Take a deep breath, without holding the air in or tonguing, exhale/play and hold a second line G as long as you can. Work your way down by half steps to low F# and then up as far as you can go without straining. After that comes slurs. I use the Irons book, but just about anything that you can comfortably play will work. Start for instance with: cececGcecececGcecGC (e=4th space, c=3rd space, G= second line, C below the staff). Then go through all of the valve combinations 2, 12, 23, 13, 123. It will be boring and take a week or two to reprogram your face, but it hasn't failed yet.