How do i get what i want!?!?!?!?!?!?!?!?

my big sis never does anything but always gets what she wants and i need help so i can do that to cuz i want an ipod touch for my bday btu i think i wont get it i have wanted one ever since the frist gen came out so please help me btw sorry if i dont type this right i am a hick!lol