I try to always think of playing as RELEASING AIR, not putting out air. We have to get to a place where the air is like something stored and ready, and you let it go at the desired time and pace. This comes with practice, and is why sometimes, if one has been out of practice for awhile, one loses contact with the air. The air feels unfamiliar and is not a part of you, so you can't release anything from you. It becomes something foreign where you feel like you have to produce it first. Then you'd have to shape it again to make it a part of you. 

Daring to release the air is a much harder concept to grasp. Indeed, we always want to hang on to something. To have true security by letting go is the key. 

Art isn't a trophy to be owned. Art is about being a part of something greater and going beyond the medium itself. 

Sometimes it's easy to think that articulation is something separate from air. But actually, when experiencing a difficulty in articulation, check and work with the air first. Very often, we actually focus too much on the tongue (tonguing too hard, tongue feels "tense" or slow) and not enough on the air. Accents, for example, should be backed up by the abdomen and not from the tongue or even embouchure alone. Otherwise the sound is killed. We end up having a lot of tongue and little remains of the sound. This can also cause slowing down in a passage. 

One also doesn't do much favor by "kissing" the sound - keep lips in place and work with the breath. Look in the mirror and one might be surprised.

Articulation is dependent on air, just like photography is dependent on light.

Keep the source of your sound production low. Involve more lower lip. Everything must come down.

We often do what may seem natural at first - "more air", "blow more" - these are the basic methods we start with as beginners when learning the higher register. This however, places the sound very high in our bodies, creates unnecessary tension in the lips and embouchure, and will be be very hard to do a beautiful and ethereal piano when needed. 

3rd register does require somewhat faster air than the lower register, but always using the minimum for the maximum result. Which means, the slowest air possible to make the sound speak. 

Just like the lighting master Felix Kunze suggests - always doing small changes to achieve great subtle differences. 

By sound quality I mean less of whether a sound is good or bad, but more of its properties. Is the sound diffused or concentrated? Brilliant or muted? Wide or narrow? Certainly though, there are qualities we more often use than others due to the demand of the music and its aesthetics.

In historical flute playing, it is important to make very fine adjustments in airspeed and focus of the embouchure. Lipping up or down is a larger adjustment, but that alone is not enough. By doing these internal adjustments, you'll have even more control and a wider range of colors/dynamics available while still staying in tune. This is especially important since we have such uneven notes like G#s, F#s, F naturals etc...Historical flute playing is working with more refined muscles on a micro-level, whereas modern flute playing is dealing with stronger muscles.

But despite the work we do on the top with embouchure, keeping an open body is still the key. Don't forget your bottom and always play efficiently.