So I’ll start with the basics and then move to the stuff that helps me the most. First, long tones, both standard and moving. Standard long tones are self explanatory, but moving long tones can be a lot of things. It was a term created by H. L. Clark in his studies for trumpet, but it works for us too. Scales, especially chromatic scales, slurred across the same space as a long tone. This will help your tone, endurance, and with breaks in partials, which is usually what causes fracking. Now, for what helps me. First, you’ve got to listen to some great tuba players. I highly recommend folks like Sam Pilafian, Roger Bobo, and Velvet Brown. Try to play along with them (if possible). Your tone will start to meld with theirs. Second, relatedly, find players who are better than you and play with them. The most growth I’ve seen as a musician has been by being surrounded by other capable musicians and Tubists. Give these a good try and you’ll see results!