Watch the Mixolydian Mode online guitar lesson by David Grissom from Open Road Guitar
My default scale in most major situations is the mixolydian mode. In this example I am soloing over a vamp in A7, and A mixolydian is the exact same scale as a D major scale as A is the fifth of D. Listen to the examples and you can hear what I'm talking about, how the D major scale sounds great over the A7 vamp. What I did was play D major scale but I resolved everything to the root of the vamp which would be an A. Here you can see that D major and A mixolydian are the exact same fingerings, they just start on different notes. The way my brain works is that it's much easier to think of A mixolydian as a D major scale with the fingerings that I showed you starting on A. By having memorized the major scale fingerings and the notes on the fingerboard it is very easy for me to see where everything lies. In most major chord situations this is the scale I will default to. Of course it's more complicated than that but in the music I play this is where I will go.