If you are not a business person, consultancies will not expect you to be a business expert -> most of your prep should be focused on the mechanics of the case, leaving comparatively little time to read tons of books and learning complex frameworks that may not speak to you (because, again, you are not a business major).
Ok, so you are time constrained but still want to learn a little bit about business. Good. PrepLounge is a good resource, economics newspapers (WSJ, Economist...) are good resources. You may also want to read one of these "business concepts for dummies" or "MBA in 21 hours" books: they will not make you an expect, but will give you a high level understanding of what is going on. After that, just practicing cases will help tremendously.
Remember - consultancies want the best minds; if you qualify, they will train you.