Modes are seven note scales which can add a lot of colour to improvisations.
If you're from a pentatonic background, trying to get into modes, it can be confusing and it seems like two different worlds. It baffled me for years, but I eventually found out that those two worlds are actually very closely linked.
I encountered some advice from a teacher called David Wallimann who simplified the theory in a way that allowed me to play modes by not understanding the theory but just by knowing where the nortes are. When you know this and you practice - then just like with pentatonic scales you start to hear when it will be best to use the individual notes in the scale.
I went from years of not understanding how to play modes to knowing how to in the space of about 20 minutes - it was one of those VERY rare ah-ha moments.
I'll start with the minor modes - Dorian, Phrygian, Aeolian. All three of these 7 note scale modes have 5 notes in common, The 5 notes are the minor pentatonic so you already know 5 of these seven notes - you just need to learn two new notes of each scale to add to the minor pentatonic. So you can still use all your bluesy pentatonic licks and just add the flavours from these additional two notes of each mode.
You will notice in the pentatonic that within the five boxes / positions on the fretboard that the number of frets between notes in the pentatonic are either two or three frets. Where those notes are seperated by three frets that's where the additional notes of the six main modes live.
The easiest ones to "know" are the Dorian and the Phrygian. The additional notes of the Dorian are one fret below the uppermost notes seperated by three frets, The Phrygian notes are one fret above the lower of the two notes seperated by three frets.
To try to make that sound simpler by example. Box I minor pentatonic - key of A. 2nd string - 5th and 8th fret, 1st string 5th and 8th fret. The additional Dorian notes are at the 7th fret on those two strings. The additional Phrygian notes are at the 6th fret.
The Aeolian is a bit more difficult. One of the two additional notes is one fret below the top most note, and the other one fret above the lower most note. In the above key of A example it's the 6th fret on the 2nd string and the 7th fret on the 1st string. I have found with practice I have now remembered the pattern for the different boxes, but if in doubt your ears are likely to be able to tell you if a note interval of one fret above the current note is likely to sound OK.
This is a David Wallimann video about the minor modes.
Minor Modes - David Wallimann
With the Major Pentatonic the major modes of Ionian, Lydian and Mixolydian work just like those minor modes I've mentioned above.
The Ionian behaves the same way as the Aeolian as to where the additional notes sit in those pentatonic notes seperated by three frets. The Lydian is like the Dorian and the Mixolydian is like the Phrygian.
This is a David Wallimann video on the major modes.
Major Modes - David Wallimann
After a while practicing these you start to hear which mode a backing track / chord arrangement might be. If in doubt try it out - if you pick the wrong mode your ears will tell you about it! A lot of backing tracks have info with them to say what mode they are. If it's minor blues the Dorian seems to be the most likely of the three minor modes.
I have hugely enjoyed the way this knowledge has opened doors to my being able to play a much more varied range of improvs against a much bigger range of musical styles, and it has also extended the scope of improvs for blues playing too. I hope it's of some use to others as well.