Hey. Basically in a Bb blues for example, its based on dominant seventh chords, such as Bb7, Eb7 and F7... or for you tenor players, C7, F7, G7 type situation.
A dominant, or seventh chord, is a major triad with a flat seven. so C7 would be C, E, G and Bb. Bb7 would be B, D, F Ab.
A blues scale is a little different., which is used to improvise also. A C blues scale, would be C, D, Eb, E, F, F#, G, A, Bb. Its a major scale, with a few added notes, and lowered 7th.
This scale would be used in a C blues to improvise (along with many other involved chord scales, but this is a good one to start with.) You'll notice a lot some of the notes sound bad or plain, like the F, while the Eb and F# have much more character.
I hope this helped, i might have went a little overboard. Anymore questions, feel free to ask. I study this stuff at the Berklee College Music, and have an extensive knowledge of various scales and such. Hope it helped.