Moving your wordpress installation from the free hosting environment at wordpress.com is tricky. So I suppose the first piece of advise would be to not host your website with wordpress.com
Why ? Because it is really difficult to migrate away from wordpress.com due to the inadequate export options.
The easiest and quickest way to export a wordpress website with all the wordpress themes and plugins is via FTP – You download over there and Upload over here – Export / import the database and providing your URLs are the same there is simply nothing else to do.
WordPress.com does not give you access to either the Database or the FTP capabilities. So you have to use the WordPress Export / import plugin which is great for posts and pages and (sometimes) media, however when it comes to Plugins, you’re on your own.
You need to install the plugins individually and set them all up with the correct settings as before, same goes for the theme. It can take days to get right.
So if you are planning on a new website hosted by wordpress.com, don’t do it if you are planning on moving host someday.