1)如果是写给机构，需要自我介绍
I am Li Hua, a boy of 16 from XX school.
I am Li Hua, a boy of 16 currently studying in XX school.
(2)如果写给亲友或师长，需要寒暄问候
How is it going?
How are things going?
How are you doing these days?
How have you been feeling/doing?
(3)说明写信目的
I am writing to you for some help.
