Biggest thing for me: have a small number of fundamental, composable abstractions. Be able to reason about how their properties interact when you combine them.

Biggest thing for me: have a small number of fundamental, composable abstractions. Be able to reason about how their properties interact when you combine them. This is the main reason that Haskell is such a force multiplier for me. All the small minutia is well defined and it frees you to think about the big picture. Sure, it's a big learning curve, but so worth it :-)