Honestly, not only am I struggling with what I'm about to write, I don't even know where I should post it.

Anyway, I took up theory not long ago and I'm trying to write a blues melody over the following chord progression:

G7 C7 G7 G7
C7 C7 G7 G7
A-7 D-7 G7 C7

At first it seemed like a simple task, then it hit me.

What key am I supposed to be in? How do I even go about applying a blues scale? I was under the impression I could only play the notes of the given chords, so where do scales come in at all?

Any help at all is greatly appreciated.
All you have to do is read the little info snippets on the main forum list and you will know. Or try the FAQs found in each forum.

This needs to go in Musician Talk.
Filth, pure filth... That's what you are.