Decision table's are really good at representing complex rules, in a language with pattern matching u can convert a nested if else block to a decision table that is much more readable, as an example see https://github.com/finos/morphir-examples/blob/master/src/Mo...
You can also use sth like Map<List<Boolean>, Result> in languages with no pattern matching. Sadly map literals aren't pretty in some of these languages, but it's still better than a bunch of nested if-then-elses or switches.
In the past I have just worked some hairy logic on a spreadsheet and just manually migrate it to code / nested conditionals.
This other article [1] shows some really cool ways to writes decision tables using structured editing UI. I wish structured editors where more commonplace!
