Being a euphonium major in college, I have found, on my own, that the most effective excercises were my breathing and long-tone excercises. The breathing would go as follows: ex. in for two, out for four.....; in for two, out for eight......; in for two out for twelve......; and so on. For long tones, I generally like to play an F on the horn, and then take the mouthpiece out......and continue through the open series of the horn. I have found that 90BPM works the best for me, but everyone is different. I generally like to warm up every morning with this excersise. Hope I helped.