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My guess is that you're already on the way. Having good concepts in your head is a big step. Be patient, give it time, and always strive for the best sound. Eventually your body will begin to do its magic and produce the sound you hear in your head.

Lots of time playing solidly in the low low range is very beneficial. The Wes Jacobs Low Etudes book is helpful. I have my students play exercises in the Getchell an octave lower than written. This transfers nicely to using an air stream with more "girth" an volume "air flow volume" throughout the range.