This is probably the most basic tip: installing the system itself! Turns out that it’s easier than you think to start using Git on your system. This tip will continue to be updated with the latest and easiest ways to install Git on your favorite operating system.
If this list doesn’t have your favorite operating system’s directions, if links have become outdated, or you have an easier way let us know in the comments! Also, if you’re having snags getting Git installed/compiled give a shout.
Windows
Yes, it works! There are plenty of awesome guides, but nathanj’s Illustrated Guide to Git on Windows is simply the best. It has a tutorial on how to get started using the system as well, and you can get started on it by downloading Git on MSys. Another option available to Windows users is compiling from source with Cygwin.
OSX
On 10.4 (Tiger), install MacPorts and run sudo port install git-core. You could also compile from source manually if that didn’t work.
On 10.5 (Leopard), it’s a lot easier thanks to the Git OSX Installer project. Just pick the latest and greatest version for your CPU’s architecture, and you’re set.
Linux
Installing on your favorite distro is quite simple:
apt-get install git-core
or
yum install git-core
If you want to compile from source on Ubuntu, Chris Olsen has a fantastic tutorial.
For more options, check out the Git Community Book or the GitWiki!