You could try R. D. Campbell 'Flight Instructor Manual' It is a completely encyclopaedic volume of teaching and instruction information. It's been around a long time (Ron Campbell passed away years ago) but it's still relevant. You cold also try 'The Flying Instructor's Patter Manual' which contains model scripts for all the air exercises.
The school that you go to for your instructor course will give you all the information you need to deliver the exercises in the way you will be shown. I suggest that you contact the school you have chosen and ask them for any material that they recommend. They will also have an insight in to what's best in the UK/EASA environment.
TOO