Starting questions for the collaborative document

We share these questions in a common collaborative document and we wait until we have sufficiently many answers to question A. But we also encourage answering other questions which we revisit at the end of the demo.

A. What does "modular code development" mean for you?
B. What best practices can you recommend to arrive at well structured,
   modular code in your favourite programming language?
C. What do you know now about programming that you wish somebody told you earlier?

Additional questions

D. Do you design a new code project on paper before coding? Discuss pros
   and cons.
E. Do you build your code top-down (starting from the big picture) or bottom-up
   (starting from components)? Discuss pros and cons.
F. Would you prefer your code to be 2x slower if it was easier to read and understand?