All Students preparing for Grade exams are recommended to use the Hofnotes on-line training pages to practise for the aural tests.
At higher grades you must be able to discuss with the examiner musical features such as texture, form, style, and period of a piece of music. My own web pages to help with these parts of the test at Grade 5+ and at GCSE are available here!
Piano technique covers everything from how you sit at the piano, and includes how you use your ears and brain, your back, shoulders, arms and fingers, and your feet.
There are some wonderful scholarly books on the subject including James Cooke's Great pianists on piano playing, which includes a chapter by Godowski, whose technique was absolutely legendary.
Joseph Lhevinne's Basic Principles in Pianoforte Playing is also excellent, as is Franck Merrick's Practising the Piano.