Letters sent to friends and relatives are called personal letters. Personal letters are usually written in an informal language. The tone and style of a personal letter should be familiar and intimate depending upon the level of intimacy you have with the person you are writing to.
Formal and elaborate sentences won’t look natural on a personal letter. Instead, write short and loosely connected sentences. You may also use conversational idioms and colloquial expressions. Contracted forms like won’t, can’t, I’ll etc. are also very common in personal letters.
A personal letter should express the personality of the person who wrote it. It should be a like friendly talk and the reader should be able to hear your voice as he/she goes through the letter.

What to write?

Your letter should be interesting to your reader. Don’t devote the whole space to yourself. Write about people your reader is interested in. You may also want to write about the things that are of common interest to you and your reader. The purpose of writing a personal letter is to make the reader feel happy so show genuine interest in him/her. If you have a particular purpose in writing the letter – say, to convey a message – state it clearly so that it would not be obscured by the other details in the letter.

In personal letters the salutation could begin with Dear or My Dear. Note that My Dear expresses more intimacy and affection than Dear. The subscription could be Sincerely yours, Yours, or Yours affectionately. Many people also write ‘love’, ‘see you’ or ‘cheers’. Note that ‘love’ is not usually used in letters written by a man to another man.

Sample Personal Letter

M 1014, Sector 17
MG Road, Mumbai
October 10, 2009

Dear Alice

Many thanks for your letter which arrived this morning. We are thinking of visiting you one of these days. By the by, how is Tom? You said nothing about him. Isn’t he studying well?

Convey my regards to everybody at home.

See you soon, I hope.

Thanks again

Yours
Ann