Asking your employer for a casual leave is a simple process. You just have to keep few things in your mind like the tone of the letter should be formal, the letter should be concise with the exact number of days you will be on leave. It should also mention the date of joining once you will be back from leave. It will be a good thing if you will give a reason for which you are taking a leave.
Here is a sample casual leave letter:
42, View Hill,
20th April, 2010
Dear Mr. Gotham,
Ref: Casual Leave Letter
I wish to apply for 7 days leave, as I have to attend a telecom conference from 23nd to 27th April. This is an important conference as I would come across with many new and advance technologies that we can use to update our telecom system. I am keenly interested in attending this conference so as to learn the revolutionary aspects of telecom industry. With the conference there will be a 2 day workshop where I will learn and see the things practically. As this conference is in Frankfurt so I need to move on 22nd in order to reach in time for the conference.
I shall be resuming office on 29th of April 2010. I will be thankful to you for considering my application.