I have a 1134 line function with zero tests defined for it sitting open in the background which most likely scores something like 32 out of 11 on that list. I'm afraid of touching that monster...
1. Create a new class for the computation
2. Define a method on that class to do the new work.
3. Copy the body of the old method over, and change variable references to instance variables.
4. Give it an initialize method that takes arguments to set the instance variables used in step 3.
5. Make the old method delegate to the new class and method.
I'm not sure if this is the _best_ example, but I wrote about this a few years ago, in Ruby: http://blog.steveklabnik.com/posts/2011-09-06-the-secret-to-...