A common problem, it seems.
My advice would be to try and relax. I'm sure you don't have problems talking on the phone, and if you can learn to treat the radio like that you will soon get the hang of it. Most people get stuck because they are trying to get the phraseology EXACTLY right. This should be the end aim, but I should just try saying what you want in relatively plain language to start with. After all, (most) controllers are human and can recognise plain speech and do not rely upon exact voice recognition like a computer to take action. Once you have got the hang of that you can perfect the standard phraseology.
Probably the best place to start is in the circuit, where the variety of possible calls is more limited and you get to say the same thing at the same place with a similar reply each circuit. This will build your confidence and you can move on to radio calls to other units.
The various mnemonics such as TRPACER which most students struggle through with many 'errs' and 'ums' as they weld their finger to the transmit button actually boil down to a very simple three issues:
WHO you are
WHERE you are
WHAT you want.
That's all you need to convey, and it is perfectly acceptable for it to be elicited in more than one transmission. Of course later you will be able to reel off:
"Anywhere Tower, this is GABCD, a C172 from Here to There,, routing via Bravo and Charlie, Presently overhead Alpha at 2500 ft QNH 1020 VMC estimating Bravo at time 45, requesting Zone transit"
but don't expect to get that all out at this stage in your training.
RELAX!!
The golden rule, however, is if you are not sure what to say next, say 'Standby' and TAKE YOUR FINGER OFF THE SWITCH while you seek help from your instructor. Or if you don't know what the other unit said, say 'Say Again'. DON'T just freeze with your finger on the switch because then no-one can do anything to help you!
It will come, honest!
