Emigrate to Australia?

Hey I wanna move to Australia. How do I go about it? I'm starting A-S level biology, physics and chemistry and re-doing GCSE french to get a B to an A star. What jobs do they want? I wanted to either be a teacher or a medical profession. I got 4 C's, 4 B's and an A at GCSE (an A and B in Science - would of re-sat the B but I got told I had an A so didn't need to) so I know I can't be a doctor though I would really like to be one. If I did a degree in chemistry/nursing and got a 2:1 or above as well as good A-levels could I do a second degree in medicine? Do Australia want doctors? When should I emigrate? thanks