Well, we do have a
creative writing thread in this forum. It's difficult to tell how you're getting it "wrong" without seeing examples of your writing so, if you like, you can always post a few samples there.
Broader exposure will definitely help, especially if you're intending to take writing as a profession. However, the "exposure" is not just limited to other forms of art or writing, but also to life in general.
Most fiction writers openly admit that their characters are partly inspired by people they know in real life. They aren't necessarily based on real people, but are often adapted from them.
Just as how an artist would study anatomy to make his drawings more life-like, an author would also benefit greatly from studying how people behave, how they feel, how they think. You need to develop greater empathy for other people, to bring your own characters to life, as realistically as possible.
That brings me to this point you've raised:
It's difficult to say whether the above is a flaw of the Western works you've read or just your subjective opinion. Examples would be helpful.
In any case, like your professor said, in modern creative writing, it's usually better to "show" rather than "tell", for the simple reason that you've already observed: it'll seem unnatural otherwise. This may sound strange, but once you get to know people very well, you'll begin to realise that we often do not "think" the way we
honestly feel.
That's why, for dramatic purposes, it's far more effective to show how your characters behave than to take your readers through a monologue. Readers relate to action a lot more easily than they do to dialogue. Speech is just a statement of intent, but will your characters really behave the way they intend? Ah, that's the million-dollar question, isn't it?
Now, it
may be a quirk of the English language or Western culture, that somehow makes "inner thought" sound insincere. I've had lively debates with a colleague over the comparative strengths of Mandarin versus English. I've observed, for example, that certain heartfelt emotions are expressed much better in Mandarin than in English. Because of the wealth of poetic idioms available in Mandarin, it's possible for a writer to say a lot, while actually saying very little.
But the moment we try to translate the same sentiment into English, it immediately sounds corny and downright disingenuous. For example, our local politicians are fond of spicing up their English speeches with flowery analogies and high-flown imagery, and the end result is almost always painfully awful. The speechs never fail to sound insincere and, worse, they always end up being tediously long-winded.
However, when a few them switch to Mandarin (or some other Chinese dialect) to deliver their speeches, the effect is entirely different, despite the same liberal use of high-minded idioms. For some reason, such speeches often end up sounding more passionate, more patriotic. I'm not sure why, but they do.
It may well be the case that most of my country's politicians just aren't very proficient in English, and end up mistaking bombastic language for linguistic expertise. If that's the case, I wish they'd just stick to whichever language they're most comfortable with, to deliver what they want to say, as concisely and as emphatically as possible.
And that same rule applies to your writing as well. Don't burden your readers with excessive monologue. Very often, they aren't necessary, because if you can
show how your character behaves, according to how he thinks and feels, then we don't really need to "hear" his thoughts at all. Readers can easily put two and two together, once the facts are known.
Hope that helps. Keep at it. Writing is a muscle that grows stronger with practice.
Lastly, if you haven't already done so, try reading
The Curious Incident of the Dog in the Night-Time. The entire novel is written in first-person narrative. Everything in it happens inside the protagonist's mind. What's interesting, however, is that the protagonist is autistic. So, what he sees is very different from what normal people perceive.
The book, in my opinion, is a prime example of "internal dialogue" that's used very effectively, and in an English novel, no less.