I'm a designer who writes mostly Sass, Less (CSS pre-processors), HTML, Javascript and usually starts off with static site generators such as Jekyll, Yeoman, etc. While working with developers who code in Python, Ruby, Clojure, I help with the templates. In my free time, I design wordpress themes and write plugins in PHP. I run grunt regularly and bower helps me with components that I need for my designs.
This means my system is littered with Ruby Gems, Python libraries, Node Modules. They are either installed via gem installations, pip, brew or npm. Now you realize that my system is a mess even though it works. I really want to do stuffs in a sane manner, the right way.
So, what are the best practices for installation and management of all the libraries, core tools, etc. for a developer on Mac OS X. Point me to resources that I can read, ponder and practice.
Here is the scenario. You're a seasoned developer and I'm your friend  who just got a new Mac OS X system. I'm a designer who will work with Python (mostly with Django), Ruby (with Rails), Clojure, PHP, Sass, Less, Compass, CoffeeScript, Git, NodeJS, Grunt, Bower, Jekyll, Yeoman and alike. As a friend, you know that I'm not a 'programmer' but a developer-friendly 'designer'. How can you help me setup my Mac? And I don't want to come back again when I get a new Mac in future, I should be able to just transition smoothly from my old setup.
Thanking in anticipation.
I am not sure what you meant by "How can you help me setup my Mac?". It seems that you are very much comfortable installing all the dependencies(gems and all) for your projects. If you want to automate all these environment installation setup then you may go ahead and write a generic shell script to install ruby, python and other stuff  and reuse when you have a new machine :) and it has nothing to do with Mac OSX or any other OS. You just need to put correct package/version to fetch and install/compile accordingly in the script. 
Would be great if you can put a specific question here in case you are facing technical problem installing any of the above packages.
Best practices for management of a developer system on Mac OS X for non-developers