It has often been said in the flute community that there isn't a magic bullet.

Some good news here: For some students, actually, including myself when I made the switch, there was and is indeed a magic bullet. Not for all my students, of course, but most.

I personally changed my embouchure in one week. Bingo, done. It was the way it was presented.

I am known as the Embouchure Guru. I teach this embouchure you may have been trying to achieve - a more relaxed one with center of lips now being the focus rather than tightened corners - via the same way I was taught: a magic bullet of puffing out my cheeks and doing tongueless attacks.

I've had students able to achieve the same using this method, but admittedly I've also had students take months. It seems to be partly a matter of how one uses the mouth when speaking and just general flexibility of the lips. That kind of thing is surely quite individual.

Releasing tension is sometimes the hardest thing to do and it was exactly that that gave me problems. It was like saying to me to hold heavy books midway rather than totally drop them on the floor. Totally dropping I could do, so to speak, but I couldn't do anything well with the explanation of "you're too tense; relax a bit." Going cold turkey - dropping the books to the ground - was what did it for me. So, in college, with Robert Willoughby, I was given the magic bullet.

And, because we're always listening for a solid, colorful tone - and achieved as quickly as possible - magic was what I wanted. And I got. Now I eagerly pass it on to my students.   Read on:

Here is the very detailed description, minus the in-person info, that will explain quite a bit as to how I achieve my own full, rich, colorful and flexible sound. 

I suggest first using a finger as a substitute for your flute; no tone expected from your finger so therefore nothing to really stop you from trying something! Blow, downward as mentioned in other posts, but allowing the air to go right into the cheeks. Tight corners gone, replaced by much more scrunching up in the center of the lips where the focus of the tone will now be. (What I missed in my teacher's attempts to change my embouchure in HS was the fact that he kept saying to relax, be looser, but nothing was being told to me that I was going to replace the area of focus so naturally you either get no tone or revert to using corners.) The stream of air will go directly down with the help also of a slight overbite to direct it. But you will be literally puffing your cheeks. 

Next try with the flute, but try first a high note to give you a really good "blow", lots of air pressure. What you will find is that, without any use of the corners pulling back at all, a fairly good tone will come out with very little adjustment. Keep trying without tonguing. As was suggested, put the flute up, place, blow. Put it down, redo the process. The higher up you go the less scrunching needed which is why you try the upper register first. The lower you go, the aperture is supposed to get bigger, of course, so therefore more attention to focusing with the center muscles, scrunching, forming the opening, takes place as you get lower. The somewhat ideal amount, being the average, will be around D2. You will find this note to be receptive to little changes as well as will show you what more bringing in of those muscles you need to do. I'm not saying it's tight, by any means, but also don't assume that this relaxed embouchure means that you are going to go limp. I think that's the most common aspect of not getting the embouchure when changing from the smiling one. You ARE focusing with muscles; just different ones.   With the use of the center muscles as your focusing area, forming a rather nice pressure directed towards the center, intonation in the middle register is also a huge improvement and statements such as "You must lower the C#" leave your consciousness altogether. The addition of the frown (although I frowned with my smile embouchure anyway so that wasn't a change for me) in the upper register goes hand in hand as well.     

From students:

"Adrianne, since the middle of August, I have been practicing the new and improved flute embouchure you kindly showed me at Boxwood. On average, I have been practicing 90 minutes a day, seven days a week.  At Boxwood, as you will recall, you spent about five minutes with me during which you quickly diagnosed the problems with my “old” embouchure and then showed me precisely how to develop a “new” embouchure that would more than eliminate those problems. I am delighted to report back that those five minutes have completely transformed my relationship to the wooden flute, and also the relationship between the wooden flute and the various other wind instruments that I play. The wooden flute (that is, my recently acquired Windward flute) is now unquestionably Number 1. As I continue to practice an average of 90 minutes a day, I am finding that the purity of my tone, the accuracy of my intonation, and my dynamic control (from soft to loud) all continue to steadily improve. Along the way, I am also discovering what an amazingly fabulous flute I have.In those priceless five minutes at Boxwood, you gave me the most extraordinarily “compact” gift I have ever received from any teacher. Your insightful attention to my embouchure problems was, without question, the outstanding highlight of my entire week at the Festival. And I suspect that that moment will remain forever a highlight in my continuing pursuit of flute-ful endeavors. It’s hard to imagine more valuable and more transformative “instruction-per-minute” than what you gave me. " 

"You’re a genius, a star, and a giver of great gifts, and I am exceptionally grateful to have met you and to have been touched so magnificently by your precise and effective teaching. The next time our paths cross, I will look forward to demonstrating to you how your instruction has radically changed my playing for the better. With ongoing gratitude, admiration, and affection."