I think the best advice that I've read so far is that a major part of it is in the volume of air you put through the horn. I was always a fairly good screamer but not much flexibility. When Brian Pennington got a hold of me, he literally threw out my Parduba 5 star double cup, and gave me a 3C. He changed everything about the way I played. No more tilting my head down and applying as much pressure as possible to squeeze out the notes. He had me lift up my chin to open the airway more. I also practiced by holding my soprano flat in my hand and playing without any pressue to my lips whatsoever. Frustration was king during those couple of months but it didn't take long until I was back to the point I was when I switched. From there it was a lot of interval studies in the mid range and always cooling down with low, long tones. Right before the season started he changed me over to a Schilke 14A4A, and I've been using that same mouthpiece ever since. My overall sound, endurance, range and screamability was so far and above my old style of playing. Once You get real comfortable with the high mid-range, it really doesn't take that more to throw in some dog whistles. Remember, no one really screams through the whole show. Just practice and like a previous poster stated, a season of marching is going to more for your playing abilities than you can imagine! Good louck!