When you're in the thick of it it is hard to see where you should split up a bit of work. Usually a couple of lines is perfect, but if you're doing something mundane like a switch statement the mental overhead might be higher if you split things up.
One rule that is easy to apply and remember is that someone in your team needs to be comfortable to replace the method within a short span of time. 30 minutes is a number to stay below.
Apply this when code is written.
Question yourself before you leave a context if the methods/functions are not too complex or too scattered.
You should see more consistent method sizes and more readable code after you've applied this as a team for a while.