Could someone please explain how to effectively utilize key and time signature changes? Whenever I try to work one into a song it just sounds abrupt or unfitting. Thanks.
Dont force it. If you hear a key change in your head, put a key change in. If you hear a time sig change, change the time sig. Doing stuff just because you want to add complexity or something is not the way to go.
My name is Andy
Quote by MudMartin
Only looking at music as math and theory, is like only looking at the love of your life as flesh and bone.

Swinging to the rhythm of the New World Order,
Counting bodies like sheep to the rhythm of the war drums
I agree with the above comment.

(I don't know if this is even worth a post but i just figured i'd say it)
“Science cannot solve the ultimate mystery of nature. And that is because, in the last analysis, we ourselves are part of nature and therefore part of the mystery that we are trying to solve.”

-Max Planck

Key changes to the dominant or relative minor generally go the smoothest, but you can theoretically change to any key. Fiddle with secondary dominants and the cycle of fifths in each key if you're looking for a progression to link an A section and a B section that you have.