Oleh
Have you been learning modes and trying hard to practice every day for many years but still don't understand how to use them? You might not even know how to identify them apart, I suggest you should comprehend it in another way. The question is, what kind of method should you use? The simple answer is the Fix-Do Method.
If you're now a "movable do person", trying "fix do" to play or identify modes will help you think far from the tonality concept. I've been using it this way since I got stuck a couple years ago, and I think it totally works!
Learning modes while still thinking in tonality (movable do) will make your brain find the similarity between one mode and another mode with do or tonica as the reference. For instance:
Dorian is re mi fa so la ti do re and Lydian is fa so la ti do re mi fa
I agree that this concept is the simplest way to understand modes, yes, it is absolutely true for only a musical theory, not for practicing and improvising. You should be aware that this way tends to suggest using the tonica (Do) as the reference notation. When you play dorian, the Re (for a movable do person) should be answered by the Do, but actually the Re in dorian modes must be the root of this scale. So, a decade ago, I changed my modes into this formula:
The Fix Do or the Movable Do Person will use the same reference, the Major Scale/Diatonic Major.1-2-3-4-5-6-7.
The first mode that I learned was Mixolydian. It only has one different notation (7b), compared with the major scale. Mixolydian formula: 1-2-3-4-5-6-7b. Moving to another mode, I chose Dorian because it has one different note compared with the Mixolydian. Dorian formula: 1-2-3b-4-5-6-7b.
Before you move to the other modes, it's better to compare the nuance between the major scale, the mixolydian, and the dorian.
After I mastered those two modes, I moved to the Aeolian mode. Even though the path of this mode is identically similar to the minor natural scale, just keep making it different because you are not a Movable Do Person anymore, which means you are not using the movable do. The Aeolian formula is 1-2-3b-4-5-6b-7b, this mode is like Dorian, shifting the 6 to 6b. The next mode is Phrygian. Using the Aeolian as a reference will help you remember this mode, the Phrygian formula is 1-2b-3b-4-5-6b-7b. The next mode is Locrian, and I think this mode is rarely played, but we should master this mode. The Locrian formula is 1-2b-3b-4-5b-6b-7b, If you're now using Phrygian as a reference to compare the Locrian, well done! Now you're moving to the fix-do concept!
The last mode that I learned is the Lydian. The one mode in the fix-do concept that uses the sharp (#). The formula of Lydian is 1-2-3-4#-5-6-7.
The next step is practice, but keep focusing on the formula and fretboard visualization. I think this perspective will help you understand modes in a couple weeks.