Embouchure can make a tremendous difference in the efficiency with which you use the air you've got. It changes according to the range in which you're playing. In the first octave, the lips need to be a bit looser, corners drawn out a bit, and blow more directly down into the instrument. As you go higher, the corners draw in, the air stream gets smaller and is gradually directed up until, at the highest notes, your air stream is practically parallel to the floor. Does that make sense to you? In other words, with low tones, blow toward the florr; mid range, blow at about 45 degrees; high range, blow practically straight out.

I seems awkward at first, but you'll improve your tone AND your capacity for playing longer phrases.

Lynn