if you are quiet familiar with the content, do pp first,
if you dun know what should be the main focus when revising, do pp first.
for me, i lose passion to revise chem books but i hv some concept for the content, so i will do ex/pp then if i dun know how to do, i will refer to textbook and do revision for that part.
indeed, see which method make u hv the great motivation.