Practice buzzing with just the mouthpiece to train your lips (and your ears) to buzz on pitch. Change pitch by changing your lip position on the mouthpiece, but don’t completely readjust. Aim lower for low notes and push from your gut. Aim higher for high notes and push from your chest.
Your embouchure is vital to good tone. Embouchure is your mouth and what its doing. Make sure your cheeks aren’t puffed out at all.
And also, when you have perfected your piece/s and you play them in front of a crowd don’t stop playing if you mess up ( you didn’t go there to practice the people want to hear you play! ). If you used the tips here and the basics of playing the trombone, you should be fine.
