Never be afraid of talking to ATC just remember
Who You Are
Where You Are
And What You Want To Do
Speak Slowly, Clearly and ATC will do the same, Speak fast and they'll rattle back the reply!
I compose the message in my head first.
I made loads of mistakes and still do on the odd occasion (forgetting to amend my call sign to messages etc) ATC will use standard phrases too if you don't understand things. I was asked once to identify over a certain VRP and i got confused told him i was squawking 1200!! ATC replied "NO Press the Ident button..... " totally understood and complied, i gringe... i even added "Rodger Pressing Ident"
You could also bail up an instructor in a room and get him to pretend to be ATC, i did this once, useful to get thrown a few curve balls like go arounds and funky approach instructions.