The Embouchure

Whether as a complete beginner or a player of a considerable amount of time, the embouchure is a fundamental part of all brass playing.  From previous experience, if the set-up is wrong then problems will sooner or later arise, and these can be an absolute pain to sort out.  These can be avoided by making sure there are no obvious problems with the set-up.

There are hundreds of muscles around the lips, pulling and stretching skin to create the aperture and common things that can go wrong are if the muscles conflict with one another, get strained, or are being misused.  

To see if there are any obvious problems, just with the mouthpiece, buzz a note and then remove the mouthpiece from your lips.  You should be able to continue buzzing that note without the mouthpiece.  Whilst buzzing, you should be able to see the corners of your lips being tight and pointing downwards.  Then try replacing the mouthpiece back on to see if the note can be produced without any fluctuations.  All this should be done on one breath.

Another thing which is mainly in trumpet players, should be to check that all the red membrane of your lips is inside the mouthpiece.  Not on the rim or poking out, the entirety of the red of your lips should be inside the mouthpiece.  These are the parts that buzz, and if your embouchure is faulty in the sense that the membrane is in the wrong place, problems will arise.

A brilliant book to work on your embouchure and set-up, building up the muscles and flexibilities is How Brass Players Do It by John Ridgeon.  It is an excellent book for all players and if you stick to it, it can sort out all your problems in no time.