I - IV - I - I
IV - IV - I - I
V - IV - I - V
Now, let's say I work in the key of A.
Notes: A B C# D E F# G# if I'm not wrong.
Which means we're gonna use the A (I/root), the D (the IV) and the E (V).
Well, how do I know which chord type I'd better use? I.e all major chords, all 7th chords (I know they provide a very bluesy sound, but wait, should they be major or minor seventh's?) or should I use a combination of all chords?
Is there a rule or two which can help me on this?