There is a lot of good information on here so I'm not going to try and reconfirm it !
Things I learnt was on a 2 day training course is worth it's weight in gold.
I did mine with a guy called Malcolm Dobson, he's ex ATC like 40 years! and does training at Barton and Leeds. I went from a oo arrr umm to feeling like RT is just something I've been doing all my life.
The RT Practical is not really that close to real life, it does the basic calls but misses all the real stuff like ATC squeezing you in between two airbuses, busy cat D zone exit clearances, odd holding instructions etc
Bits I'd add are:
Always write everything down ATC say (I use a form of short hand)
If poss ask for a RIS rather than a FIS
If your flying near an airfield an it has a frequency give them a call anyway just to let them know you are there.
If it's a long call your giving, write a crib of the items your going to say.
If your making a call to get some info, listen out on channel for someone else to ask and nick the bits that are general, like QNH.
At some airports mainly big busy ones, you can get taxi instructions, a zone exit clearance, ie direction out of the CTR i.e. via congelton low level not above 1500ft, and also take off ie, after take off early right hand turn to the south tracking to woodford.
Best plan on these is print off the ee routes and vrp's from the a/p AIP.
and lastly talk to them as human, ye there are specific phrases but if you don't understand just say so, rather loose face than wilco to something you didn't get.
And on the test, you can go at your own pace, don't feel rushed in to making the next call, prep yourself on paper before you push the button.
especial the mayday and phacer calls.
The number one best thing you can do in prep for the test is find someone to ask as the ATC and role play it. also having an atc radio to listen to is good use.
lol and remember all you learn now will be useless in 2009 !, no more FIR RIS RAS !
Best of luck Ian