You can extract it pretty much anywhere and then add the "bin" subdirectory to the path. I prefer installing it to /usr/local/java so I get /usr/local/java/j2_version_blah as my java home.
Then add the bin subdirectory to your $PATH environment variable. You can do this on the commandline like this: export PATH=$PATH:/usr/local/java/j2whatever/bin
You can also set the $PATH in /etc/profile, ~/.bashrc or ~/.bash_profile or whatever you want.
For a more thorough explanation and walkthrough, please refer to my post here