Getting a celebrity to help out your cause can be a daunting task, however if you can succeed in doing so, it will be worth all the effort and the rewards can be amazing.
Here are a few things to remember when writing to any celebrity):
Always be polite when requesting an autograph or anything else, whether in person or in writing
When writing a letter you should try to be original. Using a form letter will read like an autograph hound's request for money.
Make It Personal (for Them and for You)
Tell the celebrity what you admire about him/her. If you can't give them a few compliments you shouldn't be writing to them. This lets the celebrity know that you are not simply an autograph hound and are a legitimate fan. Site their performances, personal encounters, or mention things they have said in interviews.
Nobody likes to read negative reviews of themselves, especially when you want something in return. Compliment the celebrity enough to let them know you appreciate their work.
Get To The Point
Your letter should never be longer than a page. Celebrities receive tons of mail everyday and don't have time to read 20 page letters.
Ask A Question
It is often a good idea to include a question in your letter. Some celebrities will write a personal note or letter in reply to your questions.
Keep it Neat & Clean
It's up to you whether you hand-write your letter or type it. Handwriting may be more personal, but if your handwriting is terrible then you should highly consider typing the letter. If you are helping your children write the letter, make sure they write it. Some celebrities enjoy children's letters the most b/c they are cute, personal and original.
Use Common Sense
It's a good idea to write your address at the bottom of the letter and/or back.
Keep in mind that you may never receive a reply, or your reply may take months to arrive. These are very busy people who do not stay in one place or work on one project for very long. Some celebrities get thousands of letters everyday and can't possibly reply to them all in a month. Wait a few months before sending a second request. More than 2 letters a year is simply desperate.
Don't Be Pushy or Annoying
Never send registered mail, which requires a signature from the recipient and extra costs to you, in order to obtain a signature. Keep in mind that some celebrities have proxies pick up their mail (even if you have their home address) and legal agents who can sign for them. Some celebrities know this, and will start to return mail unopened.
Remember Your Goal
Thank the celebrity and.. have fun!
Flattery is not productive and usually self-defeating - respect, honesty and sincerity are your best friends and most potent weapons. Respect the celebrity as a person and a professional and definitely respect their time, even if it simply reading your letter. That's why you keep it precise and concise.