First, you need to get acquainted with your topic. Think of it like going on a date: you're trying to get to know the other person (your topic) without scaring them off because you're trying to talk about marriage, houses, and grandkids (i.e. your "real" research) on the first date. And, of course, once you've gotten to know them better, you're able to buy them gifts and guess what they would like, because you've taken the time to establish those little basic details.
It may seem like you're adding a step to all the other work you have to do... but you're actually just shifting where your effort is applied. Take the time here to save time later!
Just searching Google and taking a look at what comes back can be helpful at this stage, too! You still want to be careful that you're not pulling ideas from crazy sources, but for just brainstorming, you can be a little more relaxes -- you want ideas that you'll be investigating more/better with your deeper research after this.
Background information or overviews or fast facts -- you want to look up something, be able to quickly learn what the heck it is, and then move on. These types of sources are relatively short and while they may cover a lot of ground about a topic, they stick to basic who/what/when/where facts, not deep analysis.
Don't cite these reference sources -- use them while you're figuring out your topic keywords.
Books, like websites actually, exist on a spectrum: some are popular, some are scholarly. They get a little bit of a credibility edge by having to pass through a publisher, at least! They also exist on a spectrum of depth, with some providing nice introductions to topics (like your class textbooks) while others offer a deep dive into a very focused subject.