Steps in Writing a Letter of Permission

1. Address it to the authority of the person who is requiring the letter. If it's for a school trip, address it to the headmaster (but have your kid deliver it to the teacher in charge of the trip). If in doubt, use "To whom it may concern".
2. Put in a subheading. This is line below the introductory line, saying what the letter regards, for example "re: permission for joe bloggs to attend school museum trip". Underline this line, and write it in the center or left alignment.
3. Decide how to start the letter. "I hereby give permission for..." is a good way to start the main body of the letter, if you don't know how to phrase it. For legal reasons, be clear about what you are granting permission for e.g. if it's for a school trip, give the dates of the trip.
4. Sign off with "Signed this (n)th day of (month) (year)," if you opened with "To whom it may concern", otherwise if it's to a specific person or group of people use "Yours Faithfully,"
5. Sign the letter and print your name beneath it.

Tips:

You might think it looks weird that the main body of the letter is as short as the subject line and other content. That's OK, leave it like that. All you have been asked for is to give permission: do it with clarity and confidence.