This quickstart is written for Mac OSX Mavericks, and is a bit more verbose than other installation instructions. It should hopefully cover a few edge cases, such as setting your path, and configuring NPM, which can cause an installation to go awry.
# install meteor
curl https://install.meteor.com | sh
# check it's installed correctly
meteor --version
# install node
# as of OSX Mavericks, we need the GUI installer (?!)
# when a good command line alternative is found, we'll post it
http://nodejs.org/download/
# install npm
curl -0 -L https://npmjs.org/install.sh | sh
# check node is installed correctly
node --version
# check npm is installed correctly
npm -version
# find your npm path
which npm
# make sure npm is in your path
sudo nano ~/.profile
export PATH=$PATH:/usr/local/bin