What are the general principles of writing especially business writing?

The process of good writing involves three basic steps - preparing, writing, and editing. Practicing the following 16 principles will help you be a more effective writer.
1. Know your objective
Think before you write. What's your goal? Make sure you fully understand the assignment. Are you writing a one-paragraph executive summary or a five-page report? Try answering this question: What specifically do I want the reader to know, think, or do?

2. Make a list
Write down the ideas or points you want to cover. Why? This helps you get started in identifying the key ideas you want to discuss. If you have trouble getting started, try discussing your ideas with someone else. "Kicking an idea around" often helps you clarify your objective and fine-tune what you are trying to accomplish.

3. Organize your ideas
Just as it's difficult to find what you want in a messy, disorganized desk drawer, it's hard to find important ideas in a poorly organized message. Here are a few ways you can organize your ideas:
Importance
 - Begin with the most important piece of information and then move on to the next most important.
 Chronological order - Describe what happened first, second, third.
 Problem-Solution - Define the problem, then describe possible alternatives or the solution you recommend.
 Question-Answer - State a question and then provide your answer.
Organize your ideas so the reader can easily follow your argument or the point you are trying to get across.
 

4. Back it up
Have an opinion but back it up - support with data. There are a number of ways you can support your ideas, including explanations, examples, facts, personal experiences, stories, statistics, and quotations. It's best to use a combination of approaches to develop and support your ideas.
 

5. Separate main ideas
Each paragraph should have one main point or idea captured in a topic sentence. The topic sentence is normally the first sentence in the paragraph. Each paragraph should be started by an indentation or by skipping a line.
 

6. Use bullets or numbers
If you are listing or discussing a number of items, use bullets or number your points like I have done in this paper. Here's an example of using bullets.
Join the Business Club to:
 Increase sales
 Gain new marketing ideas
 Make new friends
 Give back to your profession

7. Write complete sentences
A sentence is about someone doing something - taking action. The someone may be a manager, employee, customer, etc. The "doing something - taking action" can include mental processes such as thinking, evaluating, and deciding, or physical
actions such as writing and talking. A good rule to practice is to have subjects closely followed by their verbs.

8. Use short sentences
Sentences should be a maximum of 12 to 15 words in length. According to the American Press Institute, sentences with 15 or fewer words are understood 90% of the time. Sentences with eight or fewer words are understood 100% of the time.

9. Be precise and accurate
. Words like "large," "small," "as soon as possible," "they," "people," "teamwork," and "customer focus" are vague and imprecise. The reader may interpret these words to mean something different than what you intended.
Reduce communication breakdowns by being specific and precise. Define terms as needed. The reader may not understand certain acronyms and abbreviations.

10. Use commas appropriately
Use a comma to separate the elements in a series of three or more items:His favorite colors are red, white, and blue.
Use a comma to set off introductory elements: After coffee and donuts, the meeting will begin.
Use a comma to separate adjectives: That tall, distinguished, good-looking professor teaches history.

11. Use the correct word
Here are several words that cause confusion.
 You're is a contraction for "you are" Your means possession, such as "your coat."
 It's is a contraction for "it is." Its indicates possession.
 Their means possession/ownership-"their house." There means location. They're is a contraction for "they are."

12. Avoid redundancies
It is a redundancy to use multiple words that mean or say the same thing. For example, consider the following:
 Redundant - My personal beliefs… Beliefs are personal, so just state, My beliefs...
 Redundant - I decided to paint the machine gray in color. Gray is a color, so just state, I decided to paint the machine gray.

13. Numbers
When using numbers in the body of your paper, spell out numbers one through nine, such as "Three men decided…" When using numbers 10 or above it's proper to write the number, such as "The report indicated 68 customers…"

14. Have a conclusion
Would you really enjoy watching a movie or sporting event that had no conclusion? No. The conclusion ties your points together. The reader wants to know the final score - the bottom line message.

15. Edit your work
Read what you have written several times.
 On your first read, focus on organization and sentence structure. Shorten long sentences. Cross out unnecessary words and phrases. Reorganize material as needed.
 Read it again and make sure commas are used appropriately and that there is a punctuation mark at the end of every sentence.
 Read it a third time and focus on word choice. Are there certain words that are vague or unclear? Replace them with specific words.
 Read what you have written aloud to yourself or to a friend to see if he or she (and you) can understand it and improve it in any way.

A significant part of good writing involves editing. Very few people can sit down and write a perfect paragraph on their first try. It requires multiple rewrites.

Summary
You don't have to be a great writer to be successful manager/leader. However you must be able to clearly and succinctly explain your thoughts and ideas in writing.
Strive to be simple, clear, and brief. Like any skill, "good writing" requires practice, feedback, and ongoing improvement.