Question

What are “the two main rules” for business and organizational writing?

Answer 1

Be authentic

Keep it authentic. People search for sincerity and integrity, and connect with it. The more your text sounds as though it was written by an honest human being, the greater the effect on your readers would be. They're going to think more about it, and understand it better.

Even when writing about business, write from the heart; yes. Tell what you think, and believe what you say.
Truthfully, state things as they are. If the truth is not easy, find the positives and concentrate on them. So be as clear as possible. Know your audience, and imagine how your text will affect them. Being truthful and frank is also simpler when you're writing with your readers in mind.

Say simply what you mean

Effective contact between businesses is easy and informative. Clearly, clearly and explicitly, you want to get your key messages across.

Use basic structures of the language and sentence, and short paragraphs, but do not over-simplify or compromise content.
Take the time to find the words which precisely articulate your ideas. Your readers don't care. Precisely state the truth, and justify them: do not rely on implication and innuendo.
Carefully edit and organize the text to ensure the main details clearly stands out. Your text should be accurate and concise, free from fluffy information and distractions