[andy_wrote]

I think most people would agree that writing things on paper first is a total necessity if you are writing mathematical code (I mean, are you going to do the equations in your head and type them out?), and I think the benefits to paper increase in proportion with the mathiness.

On the non-mathy side, I find it useful to take the concept of "rubber duck" debugging (which is totally applicable to original design and creation, and not just debugging) but write a "duck" document rather than talk out loud. Aside from not looking crazy, I find writing easier for thought organization.

Sometimes preparing slides can also be a nice way to really force your thoughts into simplest and clearest form. And hey, when you're done, you can present it to your co-workers.