how do I tell my boss that i'm quiting this job?

I've been working as asecretary for 6 months and I'm fed up with the pressures. My salary is low. My boss's always out of the country so i get to organise everything. He buys me nice gifts for doing a good job. He does not have time to find someone else to replace me. I've got another job that I've gotten accepted for and i don't know how to go about telling my boss that i'm quiting.