What metrics are useful when refactoring?

Question

PHP

There is a self-written CMS, it is planned to refactor the code. Analyzed the site using phpmetrics.org. I got a bunch of indicators, but where to start and what metrics to use as the main ones is not clear. Tell me who has experience behind him, what indicators and approaches to use.

Answer 1

Read "Refactoring" by M. Fowler and "Perfect Code" by S. McConnell.
It will be clear what, and how, and why.