Many brass players spend several minutes per day playing their mouthpiece in unison with a piano or keyboard. It is a great way to practice your buzzing as well as your intonation.
All you need is to sit at the keyboard and play yourself scales, arpeggios and simple tunes while buzzing along. It's not always easy to tune to a piano because the sound it so different. Buzzing along with the keyboard will help you play more in tune with the piano and with yourself.
I am associate principal horn of the Singapore Symphony Orchestra and the author of the progressive methods. I'm happy to share my experience as a horn player and teacher with you.