Are there things that we should avoid while writing?

it depends why you write. if you solely want to make money, you will write to please others. if you want to make a statement, you will write what you want to write.

At any rate, you should always be prepared for criticism and use it to the best ability you can.

With great power comes great responsibility. If you're a news writer, what you put in papers can be the basis of how other people will decide the course of history. That means what you write can influence people. With that great responsibility, you should be careful with what you write down. A writer can be dangerous.

If there's one thing to avoid by all writers. it's to avoid plagiarism. That's the first rule.

Yes, a writer can be dangerous. Not violently but rather by words, of course. A writer can misinform an audience, given that his article is full of holes. A writer can also influence other people either good or bad.

We are allowed to write anything and everything we sense but we should also know that we must go blind on issues that can greatly affect people (i.e. motivate them doing bad things or something)

And for the last question... You should freely speak and defend your speech/article by people who might question/doubt you. Unless you don't have freedom of speech (someone like the government suppressing you), you shouldn't speak freely I guess. That would make your life in danger.

Just my 2 cents.