If you're writing a culture with a lower level of technology, or with a different emphasis on technology, you have to re-think your automatic assumptions.
If your people don't have clocks, or anything else that measures minutes or seconds, or if time-keeping devices aren't commonly available, they are not going to say things like "I'll meet you in fifteen minutes." Even if there's a water clock somewhere, they still aren't going to worry about how many minutes and seconds things take to do.
If there is no light source, no moon, no stars, and your characters aren't nocturnal, then they can't see in the dark. In modern cities and suburban areas, we're used to a lot of ambient light from street lights, cars, building lights, etc. If your city doesn't have those, or your people are out in the country or inside an enclosed space, it's going to be difficult to impossible see. Your characters (unless your people have physically different eyes) are not going to be able to make out a lot of detail or color at night without a light source.
When you make mistakes like this, like having someone who's never seen a clock say "I'll meet you in fifteen minutes," it's like your world is slipping out of character.
It can also show that you're not paying enough attention to thinking from your character's perspective, and what their specific experience would be as a person raised in the culture you created. It can also be a sign of a mistake that newer writers will make, especially if they're pushing themselves to write quickly: you aren't thinking of what the character would do or say in that situation, you're thinking of what you would do or say in that situation.
Thinking is pretty much the key. If you have a plot or character point that feels awkward or forced, or a situation that can only work if your world slips of out character for the duration, then focus on that and think about what you could do differently. The chances are really good that your solution will be more interesting than the boring thing you thought you had to do.
All stereotypes are bad. Not just the obvious demeaning racist and sexist etc. stereotypes, but all stereotypes, any stereotypes. "Funny" stereotypes and "positive" stereotypes are not funny or positive, they are offensive, personally offensive. If you use them, there is someone who will read it and think you are an asshat and that they will never read your work again. They are a sign of sloppy writing and sloppy thinking.
Think about every character, even minor characters, as real people, with feelings, attitudes, a past, a future, a perspective and an agenda of their own. You don't have to tell the reader all of that, or even any of it, but you have to know it, because it should color how that character speaks and acts.
Someone posted this on Faceplace, I think: Are you really, truly an author? Try this little test This is not really a test, it's a list of characteristics and traits that...is sort of uncannily accurate in most respects. At least in my respects.
I'm way behind on things I want to post, including a kitten report, the Clarion West Write-a-thon, book recs, and so on, so I'll try to catch up next week.