I've only made a couple tiered cakes, so I'm not sure the best way to approach it. It seems if I frost the bottom layer first and then put the other one on top it will mess up the frosting and get crumbs and junk in it. But, if you do the top first then the top of the bottom layer won't have frosting on it and if you're doing each tier a different color then they'll get all mixed together.

What's the best way?

Well you need to ice seperately... never while they are put together .. then stack

Ok, that's what I figured. But...how do you keep from smooshing (that's a technical term, you know ) the frosting when you put them together?

You sprinkle powdered sugar on the bottom tier so that the icing does not stick to the cardboard cake circle that the top tier cake is on.

If your dowel rods are cut to the correct height, the icing doesn't get "smooshed."