Before the invention of modern modes and methods of communication, people depended mainly on letters to keep in touch. Old people always comment that there is a certain feeling of satisfaction that they experience on receiving a hand written letter from a near relative or friend.
Writing the date of the day on the right corner of the paper is one of the oldest style that is followed while writing a friendly letter. The significance is that the contents of the letter are in context to the date of the letter.
For example, if you say 'I had a chocolate cake today' in the letter, then the reader, who has received the letter a couple of days letter understands that you had chocolate cake a couple of days back.
Though there is no need to have a very formal salutation, make the salutation extremely warm and welcoming. For example, 'My dear Sara' or 'Dearest Sara'.
The introduction or the first paragraph, contains an inquiry of the person. You may word it as; 'I hope that my letter finds you in good health'. This paragraph indicates that you care for the person to whom you are writing the letter.
In the next paragraph, you can write everything that you want to tell the person. The key to write a good middle paragraph is to place all the facts chronologically or according to importance.
The last paragraph is the most critical paragraph, as you need to say goodbye in the best possible words. Make sure that you wish the person luck and good health, before you sign off and stop writing.
If you stay away from your family, you can write them a letter, instead of using the Internet as a tool of communication.