If you don't know about the topic that you are writing about, it's time to hit the library. Don't want to hit the library? Tough. If you want your readers to care enough about your story to read it, you need to care enough about it to make it accurate. Or, in the case of sci-fi/fantasy, you need to care enough about it to jumpstart your creativity by looking at facts and seeing how you can adapt and change them to make a new and exciting world. For example, in my stories, I researched the Assyrians and the Vikings to make Yangvaad jump off the page. Many people think that they can get away with just making everything up just because they are writing sci-fi/fantasy. The fact is that this doesn't always work. For example, I read a fantasy book in which a warrior disarmed a much larger man by sidestepping and slapping his elbow. As a black belt in karate, I know for a fact that wouldn't make me drop my sword. I would just circle the blade around and decapitate the guy. I stopped reading the book after that, and if you make silly mistakes like that, your readers will ditch you for an author who has more respect for their writing.
So how do you learn about your subject if you don't have the time to study martial arts for several years or earn a Ph.D. in physics? In addition to going to the library, you can also interview experts in the field. Many of these people love to share their knowledge with others, and can show you what resources will be most beneficial to your writing. Be sure to give them a thank you card for their help, or some other token of appreciation, such as cookies or something. You can also use the internet, although you will want to cross-reference the information you find there because many websites don't check the validity of their facts before they post them. Put in the necessary effort and your readers will love you for it.
