Few days ago I published a guest post from Emery Fletcher about Compiz for Xubuntu 12.04.
That post listed packages which you need to install in order to make Compiz up and running. Also, there was a method of starting Compiz.
Unfortunately, my own experience with Xubuntu 12.04 showed that the list was not comprehensive.
That's why I updated the post today. I also included the recommendation how to automatically start Compiz in Xubuntu 12.04.