Avoid the use of nonspecific pronouns (them, their, they, etc.) unless directly quoting a reference. The reader should be able to read any sentence out of context (or in isolation) and know exactly to whom each pronoun is referring. If the object of a pronoun is unclear, your grade will be reduced by 2% for each occurrence.
Each misspelled word automatically reduces your grade by 5%. Misspell 20 words and you will get a -0-.
Each misused word (i.e., their vs. there) automatically reduces your grade by 3%. You must carefully proofread your work more than once!!
Your grade will be reduced 2% for each occurrence of a mismatched subject and verb. (e.g., "A taxpayer are ineligible for the deduction" instead of "A taxpayer is ineligible for the deduction")
The above items are merely the automatic deductions. Other deductions -- for example: improper word choice, poor grammar (including incomplete sentences and incorrect comma placement or omission), and sloppy style -- will take place as needed.
Keep your business writing concise and clear! Content is important, but so is format, delivery, and readability.
The above may seem, to students, over-the-top on my part, but you need to get very serious with your business writing before you enter the workplace. Someday you'll thank me. ;)
Five Cs that result in better business communication
A book I highly recommend on the subject (required in BA324)