I'll take two

I'm chasing those ideals again. The Right Thing to do is to separate out your business logic from you interface. I read one piece of advice which stated that if you want to know if you've succeeded in separating out those responsibilities, it's the same answer to the question "is my app skinnable?"

I sometimes find it difficult judging where the line should be drawn between the UI and the underlying data. So my idea (which is probably similar to the skinnable question) is to write two applications side by side, that each access the underlying business code. If I've done the job correctly it should be obvious (or at least easier to see) where the shared data begins and the custom UI ends.

Similarly, while I'm writing my next game engine, I'll try to write two (simple) games with the engine simultaneously. This way I can (hopefully) pull all the common code from both games into the engine. It helps me know where to draw the line.