Changing a file's icon

I've created an icon from scratch with Icon Composer and saved it (as a .icns file). However, I can't figure out how to change a file's icon so that it has the icon I just created it. The copy/paste method described in Mac help doesn't work, as it copies the .icns file's icon, instead of the icon itself. The .icns file's icon is a standard preview document icon, with the letters "icns" at the bottom. If it matters, the file I'm trying to use this icon with is an AppleScript application that I wrote and want to put in my dock. Does anyone know how to do this?

 

Well, I figured out how to do it in a really roundabout way. AppleScript applications aren't like regular apps, as they're not directories, they are in fact files. Otherwise I could have copied the icon into the Resources folder of the application. The way I solved the problem is by copying the icon into the resource folder of another application, which changed that application's icon to the one I created. I then used the copy/paste method to change the icon of the AppleScript. Finally I switched the icon of the first application back to what it was originally. Sort of a complicated way to do it, but it worked fine.

Thanks to everyone for the suggestions.