I was asked recently, via email, about using technical words in fiction. My answer is that it's fine... as long as what you're writing is a technical thriller, or something along similar lines. If your goal is to write like the late Michael Crichton, author of Jurassic Park, The Andromeda Strain, and The Terminal Man (one of my favorites), to name a few, then by all means use all the technical jargon that such a book supports. Keep in mind, though, that Michael Crichton was a doctor and a scientist, so he knew the language.
Same with Robin Cook, author of Coma; he's a doctor, so his medical thrillers have the ring of authenticity. It's not necessary that you have a similar educational background to write a technical or medical thriller, but it helps. With plenty of hard research, many authors write about technology, science, medicine, etc., without having the credentials of a Michael Crighton or Robin Cook. If that's what you're doing, make sure you're thorough in your researching, and that you have someone knowledgeable to proofread your work so you don't make foolish mistakes.
But if it's not appropriate to your story, don't use technical words. What if you're writing a romance, and your hero is a scientist? Then sure, sprinkle in some technical jargon to make him sound credible, but don't overdo it. People reading romances want their heroes to be romantic, not spouting off about subatomic particles and quantum mechanics between clinches. Always be mindful of your reading audience, as well as your characters, when creating a story that people will want to read without having to consult a dictionary at each turn of the page.
On the other hand, you don't want to write down to your readers. It seems condescending, and can easily put a reader off. Writing down to your audience is when you feel the need to explain something that most people would understand without your explaining it to them. Sort of like what I just did. I'll give an example. A few years ago I read a passage in a mystery in which one of the characters was described as being ambidextrous. The author then felt compelled to explain that that meant the character was able to use both hands equally well. I felt insulted, and it affected the way I felt about the author and the book after that.
Bad is an adjective and badly is an adverb. When you're talking about emotions, you'd say, "I feel bad." On an episode of Celebrity Apprentice last year Cyndi Lauper said, when talking about another contestant, "Because I feel bad, she's so happy now." Donald Trump thought he was correcting her when he said, "Badly.You feel badly." Donald Trump was wrong, but poor Cyndi Lauper, perhaps intimidatd, kept her mouth shut. It didn't do her any good; he fired her any way.
"I try to leave out the parts that people skip." Elmore Leonard