When learning to play a brass instrument the most important thing to get right is the way your lips vibrate, or buzz. After all, any brass instrument will only really act as an amplifier to the sound that you produce when you buzz.
Producing a buzz is fairly simple. Rather than trying to explain this with text I have included a video showing the different steps to follow.
On the video I have also commented on how it is important to practice with a mirror so that you can see what you are doing. This is particularly important when it comes to mouthpiece placement. The best advice is to get the mouthpiece to sit as centrally as possible over the hole between your lips as they buzz. I have said as possible because it may be necessary for the mouthpiece to sit slightly off to one side so that it is comfortable and follows the alignment of your teeth and mouth shape. Remember that it is really important for this positioning to be comfortable, un-forced and produce a clear, definite sound.
The mouthpiece should only need a seal with the lips for the buzz to work accurately and produce the sound that you want. Mouthpiece practice should be done with as little pressure as possible, with a focus only on getting a seal between the embouchure and the mouthpiece. Taking this ideal forward to when actually playing your instrument is the obvious next step.
As I have previously mentioned on www.whatbrassplayerswant.com, pressure is something that should be avoided and this is definitely true with mouthpiece placement and how you hold the instrument. Sara Cawte commented about how Crispian Steele-Perkins made students practice by balancing the trumpet on their thumbs only so that they cannot push the instrument onto their embouchures, and this is a fantastic approach. Although this is difficult at first, it is definitely possible across the whole range of the instrument and Crispian is able to demonstrate this to great effect! For further examples of this visit Crispian’s website and look at the videos (http://www.crispiansteeleperkins.com/#/videos/4544763175) or search on YouTube.
Mouthpiece pressure will cause less blood to flow to the lips. Less blood flow to the lips means that they will go cold and will not be able to vibrate properly, and sometimes the lips may even go blue in colour. If you notice that you are pushing in to your mouth then definitely try the thumb exercise above. Your lips, teeth and your buzz will certainly thank you for the additional attention and care!