I'm reading uncle Bob's Clean Code and it completely revolutionizes my programming style. In this book author claims that best methods are small methods. What about controller's action methods in modern frameworks? Do you try to follow the "20 lines per method" rule, or you delegate some tasks to private methods? I don't ask about things that you can move to services and external classes, sometimes there are situations that you cannot avoid bigger code in action. Another question and another look at this problem - do you tract controller class as (some sort of) special class with only action methods, or just another regular class with private methods and own fields along with action methods?
or just another regular class with private methods and own fields along with action methods?
Yes. It's just a class, i.e. keep methods small and refactor as needed into private sub-methods (or delegate to other classes, if appropriate).
Personally, 20 lines is a good upper limit, but I try for less. Occasionally, e.g. for complex algorithms with lots of state, you might go way over 20.