One of the defining concepts of working on a Mac is that things (usually) work just as you think they should. This is the culmination of good design translated into working code. The short video that follows is an example demonstrating how easy and intuitive it is to change the icon for an application. Believe it or not, its as simple as copy/paste.
This is a great trick to have up your sleeve when working with development tools that create a default icon, for example the Script Editor. With this approach you can quickly change an icon to reflect that something visually represents what the application does. And to help, do a quick search on Google for Mac OS X icons and youll be amused for hours