I try to only sit at the PC if I'm "doing" something on it. Even in micro bursts. Shortlist of examples:
- If I'm thinking, I'll stand up away from the station
- If I need to code, I'll sit down with the purpose of coding to a goal / time window
- If I'm stuck, then again, I'll get off the station / away from the keyboard and think
- If I fire up HN, its specific - I'm checking HN for 20 mins to see whats happening, browsing some articles, then stopping.
- I try to avoid randomly tabbing back into mail clients and etc, I'd rather tackle it as a distinct thing as well
It applies pretty much everywhere though. If I want to game, I don't just sit down and play, I'll decide - take a break, 20 mins, gaming, do it. Done is done, get back on task.
The higher level thing is to hit your day / hour / afternoon period etc with a clear idea of what you actually want to get done. I find when you're carrying a bigger idea (eg, shit, i need to get this document out today!), it automagically structures your time a bit more.