1. The government firstly needs a ‘trigger bill'.
This is a specific piece of legislation which the two houses of federal parliament cannot agree to pass. A bill must be passed in identical form by the lower house and blocked twice by the senate. There must be a three-month gap between the first block and the second block.

Source: AAP
2. The Prime Minister can ask the Governor General to request a double-dissolution election.
All 76 Senate seats become vacant. Each state elects 12 new senators to fill the state spots and territories elect two each. Of the 12 state senators, six will serve three-year terms and six will serve six-year terms.

Source: AAP
3. The Governor General is expected to act on the advice of the Prime Minister and dissolve both houses of parliament.
Even after a double-dissolution election, if the Senate refuses to pass the trigger legislation; both houses of parliament can be called for a joint sitting.

Source: AAP