Whilst PANS-ATM sets out separations and a few 'techniques', the UK CAA used to publish a range of books that was effectively a training manual (it may even have been called that. It's now long gone but one of them was dedicated to approach radar. Maybe there are still copies around - you could try the CAA library to see if they've got a copy (although whether there is any way you could get access to it in some way....).