I think mostly when we talk of modes we are referring to the modes of the major scale. So if you know the major scale inside out, the you know the modes also; and I think outside learning the pentatonic and blues side of things then modes of the major scale are the next place to explore.
For example, try playing the A major scale over B minor. You are actually playing B Dorian. Or if you play A major over D Major and it becomes D Lydian, or an A major scale over E7 and it becomes E Mixolydian. They all have different 'flavours'
So if you know the major scale it's easy to work out but there are a few loose rules.... Dorian works over m7 chords, Phygian over minor chords, Lydian sounds good over major chords, Mixolydian Dom7 chords, Aolean Minor chords and Locrian....(no idea). So basically by changing the position of the major scale can change the whole feel of a progression. Or keep the scale the same and the change of chord will change the mode you are playing in. I think they call this pitch axis or something.
You can also change the mode for each chord, throw in a few arpeggios and your on your way to playing a bit of Jazz.
But don't listen to me, I've had 4 cans of Stella and the Blues scale sounds great over anything!!