Here is a high level overview for what you need to do to get most of an Android environment setup and maintained.

Prerequisites (for Homebrew at a minimum, lots of other tools need these too):

• XCode is installed (via the App Store)
• XCode command line tools are installed (xcode-select --install will prompt up a dialog)
• Java

Install Homebrew:

ruby -e "$(curl -fsSL https://raw.github.com/Homebrew/homebrew/go/install)"