I am a new user to Puzzling, and made some duplicate questions.
But it is very difficult searching for duplicates in Puzzling, because some questions just have titles like e.g. "Number riddle" or "A short, but brutal riddle".
Thank you for wanting to make the effort for not posting duplicates! Sometimes, it's really hard to know upfront, because you're posing the puzzle in a different context (random example: using a story about monkeys, while it was posted as a pirate story). By hanging around here for a long time, some people just 'remember' that they've seen the puzzle before on the site. Don't worry, this happens to experienced puzzle makers too. And it's not necessarily a bad thing; good duplicates serve as signposts.
So, first tip: try to focus on searching for the essential content of the puzzle, and not the story.
Second tip: since most puzzles here have been solved, try to search for (the essential content of) the answer as well. As @Randal'Thor mentions you can't use Stack Exchange for this; instead, use a regular search engine and start your query with
site:puzzling.stackexchange.com to limit it to search Puzzling.SE.
Third tip: if your puzzle belongs to a well-defined class, e.g. grid-deduction, you can use that to limit your search results even if you're searching for only one or two words.
Final tip: as you've seen, contrary to other Stack Exchange sites, question titles sometimes aren't a good indicator of what the puzzle is about. They often contain puns or hidden clues. You'll have to open the question to see what the puzzle really is about. That will take more time, but it could give you inspiration for more puzzles.