Originally Posted by
RatherGhastly
The best way is of course through the Trenitalia website, as you suggest.
Also, if you are traveling with a smartphone (Android or IOS) consider adding the Trenitalia app. You can buy tickets through it and bypass the ticket counters altogether. Also, using the app eliminates the need to validate the ticket when you use it. A step, if missed, that can cause a penalty if you are caught not having done it.