Changing syntax is hard isn't it?

You have to learn to be very observant of those around you, especially those you might call "characters". Most people have speech quirks and idiosyncrasies. Most younger people use slang and speech patterns of their own culture. Whereas older people tend to develop their own catch phrases almost, and unique phrasing and idiomatic usage.

If you don't at least try to base your characters' syntax on reality, they'll end up sounding very unrealistic, like the elevator example you used. No one really talks like that.

You can also vary your characters' pronunciation with unique spellings. A simple example would be someone with a casual disposition using "ya" instead of "you".

Try getting into the mind of your character, if you understand their attitudes and motives, you'll be able to think strategically as they would think in a situation. People don't just "say" stuff, there's almost always a reason (goal) why somebody words something a certain way.

Let's work from the example you were using, but focus on an elevator operator instead. Let's say he's a 35 year old male who doesn't like his job very much. He'd probably be quite short and terse with the residents in the building. He might say, "Going up?". To show his boredom, you might word it - "Going up?" he sighed, uninterested.

But what if your elevator operator was new on the job, how might he say it? "Uh..floor?" or "Hi!... Oh!, right! Floor number?"

And what if she was a friendly old lady that loved her job? - "Good afternoon! Which floor, sirs?" If she was talking to a child, perhaps - "Hello, young man. Which floor, dear?"

Most people don't use flowery, affected speech. And most people talk how you and I talk with slight variations here and there. If the speech is riddled with idiosyncrasies, it might seem as if this person had grown up in a cave. Even socially awkward people usually don't have THAT much trouble communicating in an acceptable manner. If you think of the dialogue of Sheldon Cooper on Big Bang Theory, his speech is deliberately odd for humorous effect. But if you're writing for realism, don't exaggerate speech variation to such an extent.

Though, foreigners are another story. If you're writing someone from, say, India. Listen to a new Indian immigrant on Youtube or something. Don't just write them how you imagine a new Indian immigrant would talk. Indians speak their own dialect of English, so it's pretty standard.

If you have any questions, just ask! I'm no expert, but if you gave me an example of something specific you're having trouble with, I might be able to help.

hard not it aint that much difficultness 

stick with me kid and ill havya speakin the kangs anglish in three shakes

Have you developed rules for the character? Maybe if you clearly define how a person speakes, it may help you flip back and forth. I think Joss Weedon does a good job with language construct.

And how well do you understand language? Perhaps a class in creative writing, or even linguistics can help.

I've got the wobblies in me brain. I have a sinus infection, and I'm dizzy. It's true.

There's another word I don't like.

It's not hard, just need a bit more character development (: