Mouthpiece buzzing - simple pattern 1
 

Hold the mouthpiece gently between the thumb and the indexfinger, close to the end of the shank.

Chose a steady tempo. Buzz with legato first time, then repeat with light attack on each note - but keep the note long (tenuto).
Sing or breath next phrase to get an apropriate rest. Use this singing or breathing as a "model" for the buzzing.