I have been playing with Joomla recently. As a beginner there is a tip that I find useful.
Although it is a tip that is quite well-known (Google brings more than 20 000 results for it), I will still mention it here.
If you want to know the module positions of a Joomla website, add the parameter ?tp=1 to the URL. For instance :
More Joomla secrets can be found here : http://docs.joomla.org/Joomla_secrets