To play the trombone in tune, it is essential to have a great embouchure. The embouchure for the trombone is quite simple and should look natural.
Follow these steps:
1) Look at yourself in the mirror with a neutral expression. The corners of your mouth should be firm, in the right position for the embouchure. The firmness should be similar to that of a warm, friendly handshake. Your lips should be touching lightly.
2) Place the mouthpiece in the center of your mouth, with half on the lower lip and half on the upper lip.
3) Blow air through the mouthpiece while voicing the syllable "TOE" in your mouth. Imagine that your lips are gripping the air.
Even with a good embouchure, proper posture, and a well-tuned instrument, certain notes on the trombone may still be out of tune. The notes that tend to be the most problematic can vary between different trombones, but the following are commonly affected.
Below are suggested solutions for the most troublesome notes on the trombone. There are many alternate slide positions for these notes, but many will not improve the pitch. If two slide positions are listed, the first one is the preferred slide position, and the second is the alternate.