To complete it:
2. As you noted, "addiction" is a ridiculous word to use to rewrite the sentence. My guess is that there was a transcription error which turned "addition" to "addiction". So the question probably had this conversion in mind:
He's very good at tennis and he's a very good footballer. => He's very good at tennis, and in addition he's a very good footballer.
4. It was more an argument than a discussion. => It was not so much a discussion as an argument.
As for your last question, obviously there is no shortcut.
You'll just have to continually expose yourself to examples of good writing (and cut the garbage writing you see on the internet). Simply put, if you see and practice millions of good examples, you'll be fluent; if you study just 50,000, you remain somewhere around the intermediate level, so to speak.