Identify the method or methods you will use to distribute your donation request letter. If you're using postal mail or sending the letters home with students, a full, single-sided page is appropriate. If you're sending an email, a shorter letter is more likely to succeed.
Determine a clear target for your fundraising efforts. "SMART" goals are Specific, Measurable, Attainable, Relevant and Time-limited. State clearly whether you are raising money for a certain cause or project, or aiming for a particular dollar amount.
Paint a compelling picture of the current situation and how donations will improve it. If you're raising money for gymnasium repairs, describe the leaky ceiling and warped floorboards, and then discuss the specific improvements the donations will fund.
Ask, ask, ask. Simply painting the picture without actually asking for a contribution is useless. Include a clear call to action in your letter, and repeat it more than once. You may wish to recommend a specific dollar amount (such as $25 per family), or to encourage parents to give what they can.