In business writing, there is generally no central thesis statement that is supported by the rest of the paper. That means every sentence must add new information.
Business writing is designed to be clear, concise, and compelling. Concise does not necessarily mean “short”, but it does mean avoiding repetition. Let every sentence work for you by adding new information. Conciseness also means avoiding passive phrasing and focusing on active voice.
Business writing should be written to a professional audience, not the instructor as in most writing assignments. Make sure you're writing to a specific audience, and use language that demonstrates an understanding of your audience. For example, while you would keep your language formal and slang-free in any business writing, you may use different terms and vocabulary based on who you're speaking to (think of how you might speak differently to a financial lender vs. your supervisor vs. your customer). Assignments are graded based on their "real world" application, which includes demonstrating an understanding of the intended audience.
Acronyms are often used but must be done with the audience in mind. If you are talking to a military audience then using military acronyms (For example, "a meal ready to eat" or "MRE") makes sense. However, these acronyms will most likely not be understood by a person who repairs bikes, so be mindful about what your audience knows.
When business professors were asked "what are you looking for in an excellent business writing?" their responses were that the basics are often overlooked...
Proper grammar, punctuation, spelling, and sentence structure
Information supported by sources
Professional word choice that is appropriate for the intended audience.
...and that common student errors reflect this:
Colloquial phrasing (slang)
Statements unsupported by any research
The links above will take you to separate OWL pages on each of these issues. Meanwhile, scroll on to see tips for writing in different business scenarios.