When I start a new project, I often times immediately start thinking about the details of implementation. "Where am I gonna put the DataBaseHandler? How should I use it? Should classes that want to use it extend from some Abstract superclass..? Should I an interface? What level of abstraction am I going to use in my class that contains methods for sending requests and parsing data?"

I end up stalling for a long time because I want to code for extensibility and reusability. But I feel it almost impossible to get past thinking about how to implement perfectly.

And then, if I try to just say "screw it, just get it done!", I hit a brick wall pretty quickly because my code isn't organized, I mixed levels of abstractions, etc.

What are some techniques/methods you have for launching into a new project while also setting up a logical/modular structure that will scale well?