The easy and consistent way is to use your Ubuntu package manager, Synaptic or Ubuntu Software Center. The Ubuntu repositories contain TeX Live bundles, but their names often don't match a specific package. So, use the search feature to search the package descriptions for the package name. Click to choose and install.
You could install (extract, copy) the package into your user home directory, to ~/texmf. This is an option if Ubuntu really doesn't provide it or if you would like to use a newer version. In that case, download it from http://ctan.org/pkg/packagename. There are often installation instructions available. On this site, you could additionally check questions regarding installation of packages in general.