There are standardized forms for songs, but they aren't "rules" per se. For example, a "12 Bar Blues" in C would be four bars of C, two bars of F, two bars of C, two bars of G, then two more bars of C. If you're playing with a group of people you don't know, you could say "This is a twelve bar blues in C" and everyone would know what to do.
But it doesn't have to be that way. Your progressions can be anything you find pleasing to your ear, and no one will call the guitar police on you.
Someday we'll win this thing...
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