Keep in mind the following things before you switch to writing a letter:
a letter going straight downwards without leaving any space on the left margin.
(b) Change the paragraph leaving one line-space.
(c) While writing any Formal letter, keep yourself to the point. Better start abruptly and end abruptly. This will keep you to the point. The examiner will feel convenient to get to the theme of your letter. Avoid maintaining too much formality.
(d) While writing any Informal letter, just start writing it keeping in mind the fact the you are causing the reader to feel your presence through the letter; in other words, the reader should read the letter as if he were talking to you.
(e) Always keep in mind the purpose of writing the letter and just ask yourself whether the letter will fulfil your purpose.
Look at the Format
April 12, 2019.
Subject: _______ (to be given only in Formal Letters) __________