this trompette string is tuned to d, keep your wrist straight, no limp wrist, your elbow must go all the way back with the handle action, no short cuts.
don't grip the knob, make a loose cage with your hand and let the knob rattle about when doing the buzzes
strap yourself in well, the hg must not move, press your guts into the hg to keep it very steady, any gurdy movement and the crispness of the buzz will be affected.
practice slowly and you'll learn faster
stamp your foot in time to give a solid down beat and play off beats with the buzz
practice 134 134 etc, then 123 123 etc then 134 134 again etc then 341 341 etc then mix it up till you're doing all 4 buzzes, it'll take ages but you will get it if you keep a straight wrist, if you can do it with a bent wrist then stop immedietely, you have achieved nothing and have failed the task.