There are some songs I play on guitar that could be improved, I think, by changing the key before the last verse and/or chorus. The little I remember from taking music theory a zillion years ago is that there are certain rules of thumb about what intervals of change produce the most pleasant results. (Now that I think about it, I never learned anything beyond 18th Century rules for writing choral music, so no wonder I don't remember this!)

Coupled with this question is that of which transitional chords are most commonly used to accomplish such a change. I ask this knowing full well that there are many instances in which one simply begins the next section of a tune in the new key (as is often done in reels and jigs, for example.)

Gosh! I just realized that there may be different rules dependent upon whether the key is major or minor. Are there?