Not sure if actually writing it out on paper is necessary. But along these lines I will often start my code by just writing comments explaining what the code in this file does. Then as I get into writing code, I break up the comments and insert the functions/classes below the comments that describe what they do. So sort of literate programming, but I don't usually go to the lengths that would really qualify that description..

I disagree about not using libraries. Libraries are almost always going to be better tested, better reviewed, and handle more edge cases than anything you come up with in-house. Of course if no suitable library exists you have no choice.