[Your Address] [City]
Date: [Date]
Dear [Friend's Name],
I hope this letter finds you and your family in the best of health and spirits. It has been so long since we met — I still laugh whenever I remember our [shared memory, e.g. cricket match during the summer holidays]!
I am writing with an invitation you are not allowed to refuse. My [occasion, e.g. birthday] falls on [date], and we are having a small celebration at home in the evening. It would make the day truly special if you could come. [If vacation: The winter holidays are starting soon, and Mother says you are most welcome to spend a week with us — we will visit [places] and I have a hundred things to show you.]
Do ask uncle and aunty for permission and let me know soon. Come a day early if you can — the fun begins the moment you arrive!
Convey my regards to your parents and love to [sibling's name].
Your loving friend, [Your Name]