I would strongly recommend getting hold of either the Trevor Thom (Pooleys) PPL books or the Jeremy Pratt PPL books for a good overview of what your students will need to know - plus it will focus your ATPL knowledge on the stuff you will need!
Also - go onto
www.caa.co.uk and search for "Standards Document 10" - it's a massive document but at the back the appendix has a list of about 200 questions which you will need to be able to answer - it's basically a list of what the examiner can ask you about in the Q&A section of your test.
Lastly, be happy with POH / Manual of the aircraft you are doing the course on and be able to read weather / NOTAM info
Good luck!