I write science fiction. I make up worlds and technology and aliens and all sorts of stuff. It can be a challenge to make them believable.
The best way to create a believable setting is to base it on reality. Use real science as your beginning point for your tech and aliens and worlds. You're on your own coming up with a great plot, that's a different topic.
So how do you go about creating a real-feeling situation and/or world? Learn, study, read, experience. Store them all in your head. Rely on your great database of information. No, do not spout it all onto the page when you're writing. Give us enough to ground your story or make your aliens feel real. Too many writers make the mistake of wanting to show off everything they've learned and created for the story. Save it for your webpage, for the die-hard fans who want to know all that. Put it in your story and you'll kill it with information dumping overload.
Some of my favorite sources to learn about bizarre things, science, technology, etc. are:
1. Television, especially PBS specials like Nature and Nova. If you watch channels like History or Discovery, just take some of their shows with a big dose of disbelief. Many of them are trying too hard to be shocking or groundbreaking. They push the show from real science into speculation. But they are highly entertaining and can lead to a lot of great what-if questions.
2. Magazines and online science websites. National Geographic is a great resource. It's got pretty pictures. The articles range from cultural to biological to astronomical to ecological to a lot of other disciplines. It's written on a high school level so it's accessible to almost anyone. I also love Space.com for their pictures and articles.
3. Personal experience. I'm talking about camping, hiking, travel, museums, etc. If you want to write about the oceans on a planet, it helps to have experienced at least a little of Earth's oceans. When you travel, take time to record the smells, textures, sights, colors, the whole deal. Don't forget to record how the air feels - dry and hot, dry and cold, humid, etc. Spend a moment just feeling, just breathing, just being. It's a great way to experience different environments.
4. Education. If you haven't gone to college yet, do your best to get there. And while you're there in whatever you're majoring in, don't be afraid to try out some of the other beginner level classes. Take an astronomy class, a geology class, a drawing or sculpture class, a music class, or whatever else tickles your fancy. Step out of your comfort zone.
If you aren't in a position to go to college, try a community class. Try a cooking seminar or an art class or a craft class. Many communities offer these classes in the evenings for a few weeks at a time. The cost is usually minimal. Many stores like Home Depot and craft stores offer seminars on a variety of topics. Learn how to lay tile, even if you never plan to lay any yourself.
Take an online seminar or join a club. Expand your horizons by trying something new.
And while you're taking those classes, indulge in people watching. Study your fellow students, study the teacher. Learn how to create believable characters for your stories.
Take whatever you have experienced in your life and use it as fodder for your stories. Synthesize them into something new.