I'm not familiar with books on interview techniques (although I'm sure there are).
For commercial awareness - I assume you know "All you need to know about the City"?
@Hazal has also recommended Christopher Stoakes' commercial awareness book before. I've also heard about the Commercial Law Handbook by Jake Schogger, although I haven't read it.
Those books should give you a good starting point. My advice would be to then research areas you don't understand in more detail (Investopedia/Khan Academy/Youtube) or to buy an introduction to finance book. I had "An Introduction to Global Financial Markets", although I am sure there are many more books out there.