I recommend to stay in a key (A major in this case). All the chord of the key are creating a harmony, and the scale of the key can be played with all the chords of the key. One thing to consider is to use more of the consonant pitches (a notes of a current chord), and less the dissonant pitches (notes in key, that are not chord tones). At lest begin and end phrases with consonant pitches.



Varying between major and (parellel) minor is sometimes used in blues.