Topper's suggestion is good. I got my PPL a few days before I left the UK in May and had a bit of a mental block when it came to RT.
My RT Instructor/Examiner was an ATCO and he taught me that they expect information in a particular order. Not mandatory but it helps things go smoothly
C - Call sign and Type, From...To
P - Position
T - Time
L - Level/Alt and QNH
E - Estimated time for next position
I write the CPTLE on my clipboard every time and only have to fill in the blanks.
I drove across the Nullabor Desert from Sydney to Perth 4 weeks ago and each time I was approx. 15nm from the next roadhouse or town I did a dummy radio call and worked them.
By the 5th day I was getting permission to land my F-16 Subaru at Jandakot, where there's a newly restored P51 Mustang, and, for AUS $500 you get 10 minutes in it!!!!
Practise makes perfect.