The people that'll read your letter of intent are busy people. They're in charge of bringing students in who can academically perform. They set program requirements up, then receive applications from applicants that meet those requirements. Your application and letter of intent gives them the first hint of your interest in their program. They have many letters to review; your job is to get them to choose you. Your goal is to convince the reader to accept you into their school.
Look at the school's entry requirements
Look at the school's entry requirements for the program you want to write a letter of intent for. If it's a letter of intent for matriculating there, match their qualifications with your experiences. For example, if the school you want to enroll in requires you to have a 3.5 or better GPA, and your current GPA is lower, then you won't be writing a letter of intent in for that school.
Brainstorm your experiences
Brainstorm your experiences that match the school program you're applying for. Organize these thoughts into the following categories: Academic experience, job experience, volunteer, extracurricular and personal experience. Make sure these are related to what you're writing a letter of intent for. For example, if you're trying to go back to school after being suspended for academic performance; focus your thoughts to things you've done that proves that you've overcome your weaknesses. Then brainstorm experiences you have that prove that you can successfully complete their program.
Copy and paste the school's of intent
Copy and paste the school's "letter of intent" instructions to your draft. Base your outline in this format; address the points they want you to make in your letter. Write the letter in business letter format, starting with the letter's date, followed by a space, followed by the reader's name and address. This information is available with the instructions.
Continue by professionally greeting the person
Continue by professionally greeting the person, or people, that'll review your letter of intent. Skip a space, then introduce yourself and state why you're writing to them. Follow with a statement of why you'd be a good candidate for what you're writing your letter of intent for. For example, if you're trying to come back after a suspension, explain who you are, why you got suspended, and that you want to be reinstated. Explain how you've overcame the problems that caused you to be suspended in the first place.
Present the proof
Present the "proof" that you meet the university's standards for the program, or decision, that you're hopping to get approved for. Draw on the information that you brainstormed in Step 2. For example, if you're applying for a management program, and you're a senior in high school, explain how you've used management in your extra curricular activities and your afterschool job. If you're trying to get reinstated, tell them about how you've overcame the circumstances that held you back the last time. Use a related personal experience that proves that you can continue your studies. Use your experience to demonstrate how you're going to excel with their program. Conclude the letter by thanking them for reading your letter, provide them with your phone number, and let them know that you'll be happy to answer additional questions (See Tips below).
When you tell them how you're going to excel in their program, show them how you're going to be an asset in any class, and to their school.
Always match your proven experience to the criteria for the program that you're writing the letter of intent for. If you got suspended, or terminated, from an academic program, tell them how you've overcame the weaknesses that lead to your suspension or termination.
Different schools will have different "letter of intent" requirements. This article provides a general outline of what you'd find in any letter of intent. But, be sure that you follow your school's letter writing guidelines.