One could write a series of books on this. Using functional programming techniques, using macros, writing DSL's come to mind first. More generally, trying to

One could write a series of books on this. Using functional programming techniques, using macros, writing DSL's come to mind first. More generally, trying to do what PG is doing with Arc - writing code that does the most using the least number of "thoughts", abstracting patterns as much as possible, the DRY principle, etc.