Some interesting notes here from Matthias of HtDP/Little Schemer author fame, how to do software engineering http://www.ccs.neu.edu/home/matthias/4500-f18/lectures.html and it's basically what I do, top down design, then build bottom up, which at some point during this I'll trash the spec and re-do it as now I have a better idea from building what I actually need. Repeat until somewhat satisfied with what been built as you'll never be satisfied.

I also use most of the advice here from the talk 'Effective ML', like creating an interface for everything, making failure obvious, ect https://www.youtube.com/watch?v=4l16sYRpfL8