You probably already know this, but learning George Russell's “Lydian Chromatic Concept of Tonal Organization”, or for short “the Concept” is a HUGE plus in grasping modes and their use. I'll put this out there for those who might not yet be expossed to it ...........
The general idea is that there is a relationship between scales and chords. Some scales give rise to families of chords, thus if you play that scale over those chords it fits perfectly well as one gave birth to the other. Not only that, there is a logical way to extend it that is easy to grasp. The beauty of this is not only simplifying your thinking on the fly, and thereby freeing your melodic choices, but also it lends itself to analyzing any music you come across in a very simple way making it far more understandable.
The very basic of it runs like this – take a scale, rearrange the noted in to thirds starting with the root of the scale and thereby get a massive chord – now look at the all the chords contained in that massive chord – the scale will go with these chords. For example, if you take the Lydian scale, rearrange it in thirds, you will find the following chords, Maj, Maj 6th, Maj 7th, Maj 9th, etc. Thus we say the Lydian scale gives birth to the Maj family of chords and fits perfectly well when we play this scale onto of any of those chords. In a like way, if you rearrange the Mixolydian scale into thirds you find the following chords, 7th, 9th, 11th, 13th, etc. Thus the Mixolydian scale can always be used perfectly well over the 7th family of chords. In the same way the Dorian scale is related to the minor family of chords.
The theory extends well beyond that in a simple way via an interesting observation. If you take the Lydian scale, starting with the root of the scale, you can arrange the notes as a series of 5ths. For example in C Lydian your first note is C and your second note you pick a perfect 5th above C, which is G and is in fact a note from the Lydian scale. You then go a perfect 5th above G and again its a note from the Lydican scale. In fact the odd thing about the Lydian scale is that in this way it turns out to be a grouping of notes that can be arrange wherein all of them are a ladder of perfect 5ths! Now the thing with building a ladder of perfect 5ths is that we can just go on selecting perfect 5ths, one above another, until we have gone through every single available note there is (in modern western tonality) before ever coming back to using the same note twice. The Lydian scale is nothing more than the first seven notes of this scale.
Noticing that brought up the idea – what if one took the next note from the ladder and used it in building a new scale. Given all letters have been used, it is an accidental of a letter already used, thus you replace the one already used with this new accidental one and you have a new scale. If you take this new scale, arrange it into thirds and look at the chords you find its chord family and all that. But what is really cool about it is how often that new accidental is used in music already. That is people write tunes and jam away on them but when they start going a little bit to the outdoors, it is exactly that accidental which they near universally pick first. Of course that new scale has all its modes and thus all its family of chords and thus you see how it fits in overall to the tune that's being played.
Now you can build yet another scale by picking the next 5th above that one and making the replacement. That scale then becomes slightly more of an outdoor sound than the scales before it. You keep doing this for some time to get increasingly more outdoor sounds. There is far more to it than just this, but it should give an ok idea of the sort of structure of the elementary part of the theory – and it does turn out that with a very, very simple rule set you can always find scale familys to pick on top of any chord played no matter what that chord may be, which in turns unleashes a ton of freedom because you not only know right away what scales you can use on top of that chord, but in addition have some understanding of how fitting they will be or how outdoors like they will be even prior to using them – leaving the rest to your art and imagination. You see, your not chancing after the rules of classical harmony here as you go, or limiting yourself to only painting in one color such as a pentatonic scale. Of course you can still play 90% pentatonic if you wish, but you you will know how to weave in and out of more far more colors if you choose to.
The Lydian Chromatic Concept of Tonal Organization – well worth the effort to grasp for sure.