Another top-tip:
If you can record your RT, either through the a/c intercom or through an airband radio. Listen to it later and work out what you wanted to say. You'll be surprised to find your RT is better than you thought and it will allow you to iron out those little snags we all get from time to time.
Most professional pilots are good at RT because a) they do it regularly and b) they have a good idea what is coming next.
If all else fails squawk 7600
(only joking)
[ 04 October 2001: Message edited by: Fox-1 ]