One point I'd share is if the code is built in "modules," and when I say that I mean that you can change one thing in a module and easily have it working with the whole. It eliminates effects between unrelated things. Also:
- Code is easy to reuse
- Your code is flexible (this ties in with building in modules)
- DRY - Don't Repeat Yourself
I highly recommend reading, The Pragmatic Programmer.