A lot of the theory has to do with innovation, emerging technologies, effects on the individual, society, environment, success on innovations etc. There are a few things on marketing and management that you will also need. As for studying do past papers but that will only do so much for you, you need to find a system to memorise the lists of factors, steps etc. so for example, for my DT students I use certain acronyms that help them and you also need to know how to make an effective plan for your section III. I'd also recommend using either the Excel or Cambridge textbook as I found them the most useful. If you need any advice just PM me