A great song is about more than just having interesting parts. That's enough to make it good, but to become truly great, you need cohesion: Each part should flow seamlessly into the next, properly managing listener expectations and crafting a dynamic journey, but that's... I mean, it's hard. How do you do that? The answer depends a lot on genre, style, and what the song is trying to say, but there are some general techniques that get used a lot, so let's pull back the curtain on section transitions and see if we can find what makes them work.