Do I need to have itinerary supporting document when apply visa?

Do I need to book flight and accommodation first and then support them for application? I really don't want to be refused when I already booked flight and hotel? What do you suggest? Was there any case that applicant was refused even they ald book flights and accommodations? One more thing, I'm an international student in Australia ( Vietnamese passport),so my financial condition is not really strong. Is it a matter for getting it? Thanks