[mtkd]

Anything that takes you away from the problem will help.

Take a shower if you don't have long.

I recommend walking before taking on a big problem - even if you're not stuck.

A 1h walk means you are unable to code your first solution, by the time you get back you'll be 4 iterations on in your head - you've just saved yourself 2 days.

[genwin]

I too find that planning code while in the shower or during a walk is much more effective than when at the computer or whiteboard.

[Rickasaurus]

Even just going to the bathroom without the smartphone can be great for ideas. Nothing beats shows though!