From a purely "good taste" standpoint, I'll throw in that it always helps to make the guitar do something different from what the vocals are doing. Contrary motion: when the vocals go up, make the guitar go down. When the vocals are resting, play something more active on the guitar. Call & response. That's a really basic idea and true in any art form.

Think of it like a movie: the camera focuses on an actor saying something in the foreground, then switches its focus to someone standing in the background (the first guy goes blurry), who says something that compliments or conflicts with what the first guy said. Don't keep everyone in focus all the time. It creates depth. It's kind of like making one boring, then the other.

In my opinion, you wanna avoid "Iron Man Syndrome," where every instrument is playing the same melody and rhythm. Then again, that song sold a *few* copies, didn't it?

Showalter is definitely the master of this stuff. His solo material is fantastic, with the way he weaves all the instruments together with vocals.

-Carl.