I use LOI's a lot when I am trying to buy a property for much less than what the seller says they want, more flexible terms than the seller says they want OR if I am unfamiliar with the property and area I will use the LOI to start the negotiating process while I do my due diligence work in the background. Remember, most of the time an LOI is not a formal offer but mainly a point of understanding between you and the seller.
In the body paragraph you will basically express your interest in taking admission. Important things you are going to mention include the basis for applying to the school. Why do you think this school can build up your career? List down all academic achievements and special skills that would help in making your letter stand out from rest of the applicants.At the end you should sign off with "sincerely yours" or any other related salutation.If you are applying for a particular job then you need to create letter of intent that contains the following.