The first thing, which isn't specifically about Joomla, is to make sure you test anything else on the domain you are installing Joomla with. The .htaccess file will change the way that things work and it is possible that existing content may be rendered unreachable. It isn't a big deal to fix though.
The difficult thing about Joomla is that you have to keep up with menus, content and modules. Make sure that you install Joomla with the setup content so that you can play around with things that currently work rather than try to add something correctly.
Templates will have different module locations. Make sure that you know where they all in order to get the most out of your template.
Feel free to PM me here is you need any help figuring something out.
