To,
Name [name and surname of the recipient with appropriate salutation before it]
Address [address of the recipient]
Date [date on which this letter has been drafted]
Subject [mention the subject precisely as in the kind of declination]
Respected Mr./Miss/Mrs. [surname of the recipient with appropriate salutation before it],
First paragraph: [in the first paragraph mention the purpose of writing the letter. Mention the kind of application made by the recipient that has been declined]
Second paragraph: [You have to mention the reason for declining the application. The sender also needs to inform the kind of checks done by him that made him come to this conclusion. The shortcomings of the recipient that resulted in declining the application has to be mentioned]
Third paragraph: [You can also mention that you feel apologetic for the decline. Wish the recipient all the best for his future]
Yours sincerely,
Name [name of the sender]
Designation [designation of the sender and the organization in which he is working]