I'm doing Product design as well........The thing that i found that will really help for your AS exam will be revising and being confident with materials, their properties, why they are used and how they are manufactured into specific materials, the finishes and also advantages and disadvantages if the process and materials I.E plastics, PET (polyethylene terephthalate), lightweight, blow moulded, expensive start up cost and so on
Try to give 4 properties and explain
A2 your best bet will be to revise the design movements and also sustainability and apply your knowledge from AS to the exam and your answers, this is what i did and what ill do for my exam this Monday
Good luck!