I sketch stuff in a notebook (a whiteboard is better, when I have the luxury). If I'm doing graphical stuff (e.g. UI), it's mainly crude layout and interaction

I sketch stuff in a notebook (a whiteboard is better, when I have the luxury). If I'm doing graphical stuff (e.g. UI), it's mainly crude layout and interaction diagrams. If it's something more logic, I try and describe the high level view, then informally break it down. Either way, at some point, I find a good place to start hacking and I feel the urge to say it in code (mainly Python, currently). When coding, I start by doing the smallest thing that I can run and verify in some way. I keep adding stuff in small increments. I only get back at the notebook when I can't think of, or decide, what to do next.