You need to understand, that you have to follow specific format, in order to write a good application letter.
Yes, you have to say things in a short and precise manner, since an application letter comes under the category of Formal Letter
I am writing the following letter to the Principal requesting him/her to issue school leaving certificate
Hope, it helps every single one of you.
City Montessori School,
Subject (Request to issue school leaving certificate of my daughter)
I am X (Your name), who is now an ex student of your school (Class 12th passed) requests you to kindly issue school leaving certificate
Kindly issue at the earliest as the date to submit Transfer Certificate in the college is nearing and I need to submit it as soon as possible, in order to avoid any last minutes problem.
I will be highly obliged,
Class 10th Student