Hi and welcome to the forums

I only joined a year ago and now can't keep away!
Even though I started piano teaching nearly a quarter of a century ago

I still remember the lead up to the first lesson I gave. My mother was teaching at the time and I used to sit in and observe her lessons on a Saturday morning. So I would suggest finding a local teacher you can trust and see if it is possible for you to go and watch him/her in action. Organisations like EPTA might be able to help.
Re books: I'm going to be accused of being old fashioned but there is a book called 'The Young Pianist' by Joan Last, first published in 1972, but the pedagogical principles of piano teaching are very sound. Also along similar lines is Fanny Waterman's 'On Piano Teaching and Performing'. I would suggest these for the technical aspects to introduce in a first lesson for a beginner. You have a PGCE so you know how the delivery of lessons will have changed over the years - it's not the book but how you present your ideas that matters - but you need the ideas first - if that makes sense.
For up to date material on how to relate to pupils one-to-one etc you have the ABRSM book and there is another one by Lucinda Mackworth Young called 'Tuning In' which has some very sound advice. And there are the ABRSM courses and taster days.
If it's any help the tutor books I first used for beginners were 'Tunes for Ten Fingers' by Pauline Hall and 'The Green Schaum pre- A'. I still use them but there are simply masses of resources out there now which are fantastic - especially when the pupil has got a little beyond the very early stages.
Good luck - let us know how you get on