I've never planned more than a few features ahead without having to revise the plan heavily. Instead, I prefer code that I can change easily. This is exactly how I avoid rewriting.

When I program, I continually ask myself two questions. The first question is does this work as I need it to work? and the second is is this as simple as I can make it right now?. My goal is provably working software that's as simple as possible.

Simple is a loaded term, but I mean that my code should only be as complex as necessary to pass the tests. Part of that comes with experience. Part of that comes as I recognize more and more patterns in my code. Since I have oodles of tests, it's reasonably cheap to continue to simplify.

Because I work in small steps, adding one feature at a time, always testing and always simplifying, I'm confident that I'll always be able to add new features relatively inexpensively. It's also nice to say, "I'm done already? I can't think of any more tests to write. The feature works. I wrote far less code than I thought I would need."