Sit up straight, on the edge of your chair, with your feet flat on the floor. hold your horn up to the correct angle, if your arm starts to hurt take a short break.
Make sure that the bottom lip is the anchor of the embouchure, the upper lip should never be under more pressure than the bottom lip.
When playing a phrase focus on a point ahead of you somewhere on the horizon and play to that point, keep your mind on this especially if you feel yourself running out of air.
If you find yourself losing control of your sound or getting lost refocus by singing your part.
Switch to the thumb fingerings for the F to A interval.