Keep an Embouchure in the Low Register
Make sure to keep a legitimate embouchure and structure in the corners when going into the low range. Many players allow their corners to completely collapse when reaching into the low trigger and pedal registers. Always make sure that there is some degree of structure in this range. Otherwise, the tone will become "woofy" and unfocused. If you have a problem with maintaining structure, try the following exercise. Play a one octave descending Bb major scale starting on middle Bb. While doing this, take note of the structure of your embouchure. Next, play the scale again, only this time one octave lower, while using the same corner structure you had in the upper octave. Try your best to make all of the adjustments happen within the rim of the mouthpiece rather outside of the rim.