If trying to learn RT for the UK then listening to an American feed is a complete waste of time, there are too many differences and that will only complicate matters.
Whilst you will hear errors on the RT if listening in you will still learn , many of todays airline pilots will tell you they started off with a scanner. There are all sorts of legalities involved see here;
http://www.pprune.org/forums/showthread.php?t=206063
Best way though is to practice practice practice. I'm told by many PPLs that they do it in the car on the way to an from work and at any other convenient time, people may look at you oddly but you will soon get it in your head.
It is a lot less complex than people think it is as well but for some reason many fear it.