When you review groups of documents you have identified, consider the context or big picture, how your topic relates to the circumstances or situations that surround it. This can help you determine if something doesn't make sense.
Let's say you are designing a solar-powered space vehicle. You want books and articles on solar powered vehicles and case studies related to using solar power in outerspace. You may also want to consult:
Can you assemble a collection that reflects both the narrower and broader aspects you need? Start with a list of questions that can help you place your topic in context.
If you are researching solar energy, you want to be sure you know how this type of energy fits in with the big picture of global energy consumption.