Only way to really learn is through your flying. So many times in my training had I practiced over and over again the correct way to say things only to fluff my lines when it mattered in the air... ATC are really helpful (at least from my experience out of Southend airport).
Remember even the pros get it wrong from time to time as the standard of some of the RT from some of the commercial traffic I over hear sometimes leaves a lot to be desired....
As others have pointed out get an airband radio and listen in, if anything it makes you realise that your not that bad after all.