In  the preface in Setting Up Drills  H. L. Clarke says:
 

Preface

During my professional experience of many years, I found it, advisable to change my method of playing the Cornet and Trumpet a number of times. My constant aim was to produce proper results in an easy manner and through a common sense method of playing; also by practicing in such a way as not to tire or injure the lips, but to strengthen the muscles of the latter, a little more each day, and in this way, building a proper foundation, in order that the regular work of a professional musician, obliged to play in the afternoon or evening, would not be impaired by too much morning practice. To overcome the usual effort resorted to by so many players in their daily practice, requires considerable mental training on the part of the student, such as keeping his or her mind on the work in hand; thinking each note as it is being played, and above all to stop imagining that what is required is hard work, but, that the practicing the student is required to do is merely taking part in the building of a substantial structure for the future.
These exercises have been my morning "setting up Drills" for years, to keep up the elasticity of the lip muscles, to produce a clear musical tone, to control the wind power properly, to relieve the constant pressure of the mouthpiece against the lips, and to facilitate correct technic by training the fingers to respond with the proper agility necessary for clean execution. One word of advice? practicing should never be continued when the lips are fatigued or tired, but there should always be a frequent rest for a few moments between each group of exercises, to keep the lips fresh and responsive. This method of practice requires the three principals of success, Ambition, Patience and Tenacity, and by perseverance all players who follow the instruction given with these exercises, will acquire the knack of playing easily, making their work a pleasure instead of a torture. I have enjoyed playing the Cornet after finding out how to practice without tiring my lips, and what I have done, others can do.

EXPERT ADVICE

To develop into a really competent Cornet or Trumpet player, requires a thorough understanding of the most and important requisites for playing these instruments, not only in a correct manner, but also with that ease and confidence necessary for all soloists to obtain an impeccable performance. For this there are seven vital points to master. Each of these must be trained separately and with the particular purpose that after the proper practice has been given to each point, they will function together naturally and intuitively.
These points which are so vitally important in the development of correct playing are:

ONE - The Lips, which vibrate to produce the tone, which may he compared to vocal cords of a singer, who could not sing properly if they were callous.
TWO - The Muscles of the Lips and Face, which must be trained properly and accurately, for the different intervals in music within the compass of the instrument.
THREE - The Tongue, which produces the different articulations and methods of attack, and which must function with the muscles of the lips when contracting and relaxing.
FOUR - The Left Hand, which must hold the instrument firmly, but in the meantime always keeping the wrist easy and supple.
FIVE - The Fingers of the Right Hand; each of these must be trained separately, in order to gain complete control over them, and enable acquisition of final technical perfection.
SIX - The Air, which passes through the lips causing them to vibrate.
SEVEN - The Wind-Power; this is really the most important factor of all and the student must learn how to control the tone for both loud and soft playing; also for low and high tones, and how to apply just the proper amount of power necessary for producing each semitone from low F-sharp to high C above the staff.

These seven points must be perfected by proper practice, one at a time, before the student can possibly expect to become a first class player. One reason why so many players fail in their work, is that they give too little attention to each of these points in their practice, trying to learn them all at one time. It is impossible to keep the mind on seven things at once; the student must learn to control one at a time, then another, until he has perfected all seven; after having accomplished this, his playing will be correct and enable him to derive the necessary satisfaction therefrom.
The above might be compared to a machine having seven parts and each one of which must be faultless before it will function perfectly. The slightest little imperfect part, any loose or misplaced screw or cog will cause the machine to stop and operate incorrectly. The same applies when playing an instrument; in order to become a really competent player, each of the above mentioned points must be perfected beforehand.
It makes no difference whether your lips are thick or thin if the muscles of the lips and face are properly trained, together with the correct control of the wind-power. To produce the best results the lips should vibrate equally in the center of the mouthpiece, so that the quality of tone is exactly the same in all registers low, middle and high.
By placing the mouthpiece one-third on the upper lip, and two-thirds on the lower lip, the middle and high registers are clear, but the lower tones are thin and impure. The other way, placing two-thirds on the upper lip and one-third on the lower lip, the middle and low registers are clear, but it causes a strain to reach the high tones, which sounds as if you were struggling and making an effort, and it requires years of hard practice to overcome this strain, and even in the end you will never play easily nor be sure of the highest tones.
Now let us take the happy medium and place the mouthpiece so that the two lips vibrate exactly in the center, one-half on the upper lip and the other half on the lower lip, equally, so that the low tones are rich, the middle register clear, and the high tones brilliant, which will cause every tone in the compass of the instrument to be musical and free from that pinched and squeezed tone so often heard.
As the upper jaw is stationary, the upper lip becomes more or less the same. While the lower jaw being movable, the lower lip moves in many ways, is the most supple and really does the most work of the two. The upper lip being the sensitive one, should never be abused by using the most pressure upon it. If you must use pressure, and it is necessary at times, especially when playing very loud and in the upper register, confine it to the lower lip, which will stand more abuse without tiring, and this allows the upper lip to vibrate naturally. Don't tie it up with too much pressure, which will stop the vibration, become numb and cause all kinds of disappointments.
Shape of the teeth has little to do with this great "machine." Sometimes a player will resort to placing the mouthpiece slightly on one side of the mouth, either to the right or left of the center, on account of a protruding tooth or an uneven set of teeth. This will not effect one's playing if the muscles of the lips and face are properly trained, and it will give comfort to the player. 1 have known many players having false teeth, upper and lower, after they have trained the muscles of the lips properly, with their wind-control, who can play wonderfully well, with much endurance. The celebrated cornetist, Liberati, also Ben Bent, had false teeth, and these men were about the best soloists I ever heard.
Be sure to read all these comments with care. Try to derive a common sense idea of everything and use your brains in thinking over all suggestions. Try to get away from tradition and superstition, which has ruined so many players. Let each student remember that theory is good in its place, but that science proves results, and that each one should experiment with him or herself, along lines of the above offered suggestions.
Below is an example showing the movement of the lower lip; it illustrates the lifting and lowering of the latter according to the different intervals and using the same method of contracting and relaxing with the movements of the lower lip. The simple, little exercise is one of Arban's in the beginning of his celebrated method. I have used this exercise, which every Cornet player knows, to demonstrate as far as possible with the help of lines under each note, how the lips move for the different intervals; this instead of blowing more for higher tones and less for lower tones, or pressing the mouthpiece against the lips while ascending. There is no visible pressure necessary in the entire exercise, just the slight lifting and lowering of the lower lip, according to the melody.
This suggestion should be experimented with, and played softly, so as to form the habit of keeping the lips in motion while playing. This will train the lip muscles properly, and will relieve the tension of the lips, in order that they will never become numb and useless.

This exercise may also be used to control the wind-power by playing the entire 16 measures in one breath, at a metronome tempo of 120, four beats to the measure, ordinary march time.
This must be done by taking a deep, full breath, playing softly and conserving the air in the first four measures, in order that the player will be able to finish easily. With such practice, it will be possible to play the exercise twice in one breath, and playing the exercise many times as explained, will help in acquiring endurance and self-control. Such practicing will conquer the inclination of taking breath whenever the player feels like it, and will form an excellent habit from the very beginning, not to take a breath until all the wind is exhausted. When inhaling for a full breath, the player's chest must be expanded, and this position kept throughout the exercise, and all the time, while the practicing is kept up.
After playing this exercise about two minutes, stop and rest a few moments. This should always be continued during the practice time, as it will allow the blood to circulate through the lips, keeping them full of life and strengthening the muscles of the lips and face. Playing after the lips are all tired out, should never be continued, as this will weaken instead of strengthen them.

The book is published by Carl Fischer (Calistenic Exercises 02282)
Copyright 1929 by Herbert L. Clarke