Tune before you play, but after you warm up. Tune to a concert A or concert F.^[1] If the tuner says you are sharp (moves to the right), pull out the head joint. If you are flat (tuner will move to the left), push in the head joint. Try tuning to the low and high A. Take into account that cold temperatures will cause an instrument to go flat, and warm temperatures will cause it to be sharp. This is especially important if you are playing in an ensemble.