Some documents to keep you busy:
UK CAA Standards Document 10(A)
UK CAA Standards Document 19(A)
UK CAA CAP 413 - Radio Telephony Manual
UK CAA CAP 804
Commission Regulation (EU) No 1178/2011 (EASA Part-FCL)
AMC and GM to Part-FCL which contains the PPL syllabus
Revise PPL Theoretical Knowledge to a good standard (see Standards Doc 10 and AMC and GM to Part-FCL for knowledge level expected)
Flying Training Instructor Manual by R D Campbell
AP3456 Royal Air Force Manual Flying (volume 1 only - Principles of Flight)
On-Track Aviation EASA Instructor Manual (Part 1 and 2)
Aircraft POH and Checklist