Watch the Dorian online guitar lesson by Robert Renman from Blues Booster
This scale works great over minor chords. It's one that I primarily use for most minor chords. Compared to the Natural Minor scale (Aeolian), it has a Major 6th. That's the only difference. Let's also compare it to the Mixolydian. We can see that the only difference is that the Dorian mode has a minor 3rd. That's what makes it a minor scale. So, if you use the Dorian over a 7 chord, just bend that 3rd a bit and you have the Mixolydian. In blues, you can get away with almost anything, and playing a minor scale over a 7 chord is good example of that. It works well, as long as you do it tastefully. Just don't use the major 3rd over a minor chord - it will not work well. I also recommend you spend time listening to the sound of Dorian, and get it in your head. Note that the notes of Dorian are also present in the Hybrid Scale, which is interesting.
*Please note that around 2:22 in, I said "Major 2nd". That was a mistake, I meant to say "Major 6th".