I disagree with the bit about liveatc.net, to me the best way of learning what to say and when, go on liveatc.net and look up an aerodrome in class D airspace or buy a handheld scanner and sit near the airport with the appropriate frequencies tuned in.
Personally I'd start with Camden YSCN (for NSW people at least) because it's not terribly busy and the feed is just the single frequency for the tower. Just listen for a bit then grab a map and follow a particular aircraft or two through what they're doing, where they are and what heights they need to be at, etc.
Once you understand that move to somewhere like Bankstown and do the same thing. Bankstown does have multiple frequencies blended into one but pick the right time of day and it'll be beneficial.
It certainly saves sounding like a fool when you go to do it for real and forget what to say or just read off the sheet without actually knowing what their response means.