About the usage of "the" (or situations where it shouldn't be used).

Hello. I have been speaking English for about 10 years now, but even now, I have a constant problem of over-using the article "the" or sometimes "a" in places where it shouldn't be! I already read up on it, so I have a good idea of when it SHOULD be used, but it doesn't mention when it should NOT be used. There are also these unspoken rules that I can only seem to learn from asking around, such as "you don't use it in front of a proper noun". Example: I am Iron Man, not I am the Iron Man.

I also got corrected on this sentence from my recent report:

"The impact of this on (the) society is threefold."

(The) shouldn't be there.

I know this sounds really dumb, but I've embarassed myself too many times in public and on college reports, and I want to get it perfect once and for all! If someone can tell me what I'm doing wrong, and when articles SHOULDN'T be used, i'll be very very thankful!

PS: if you saw any grammatical problems in this post, could you also point it out? Thanks you (I suck at writing in general)!