Leave letters are formal leave applications, written to get sanction of leave.
Leave letters are generally brief and to the point.
One must clearly state the number of days of leave required, mentioning the exact dates of leave requisitioned.
One is also expected to give a valid reason for the leave. For example, a visit to the dentist could be your reason for leave as seen in the Sample leave letter.
If your reasons are personal and cannot be specifically mentioned, you may explain as much in the letter, stating personal reasons as the cause of your leave of absence. In such circumstances, one is not expected to go into details.
Leave letters are formal letters so, the format as well as the tone and content should be suitably formal.
One must always remember to thank the addressee before formally signing off.