Business letter has great official value. You have to consider many things while writing a Business letters.The basic things you should consider are:
1.Sender’s address, date of correspondence should be correct: Normally business letters are written on the business letterhead itself. So the company name, address and contact details are mentioned there. If you are not writing the letter on the letter head, mention the above mentioned details before you proceed.
2.Details about the recipient: You should address the person whom you are writing by name, or in some cases you have to write the details such as, name of the person, his/her designation along with name of the department.
3.Body of the letter: Divide the body of your letter in small paragraphs. Always write to the point. Write in simple language.
4.Closing of the letter: This is the concluding part of the letter. So do not forget to thank the person. Convey your regards in a humble way. In case of a letter of apology, end the letter with a, sorry for the inconvenience or sorry to bother you etc.
5.Enclosures: If you are enclosing the documents, mention about the same in a clear understandable manner.
Now that you are aware about the basic formatting of the letter, you should now know about the presentation of the letter. Here you should pay attention to the font size, alignment, header, footer of the letter etc.
If you are using tables and bulleted points wherever required, it gives a concise look to the letter and can highlight the relevant information.
You will find a lot of information regarding, how to write business letter? types of business letters, sample business letters etc.
Business letters are categorized in many types such as:
=>Proposal letter
=>Follow up letter
=>Request for proposal / Tender enquiry
=>Inter company or Intra company correspondence e.g. memo, notice, letter of appreciation etc.
=>Business thank you letter
Business letter is preserved as a document for official purposes, so it should be precise and correct in all respect. In many cases the letter reference number is also included in business letter that contributes a lot to maintain and refer the record at any point of time.

I have posted article for business letters.this site contains different types of business letters like Business thank you letters,apology letters,etc