You will note on the student visa you are issued Condition 8101 appears..
Condition 8101 states, The holder must not engage in work in Australia

In order to obtain a new visa with permission to work, you will need to commence studies and request your course provider to provide you with evidence of your commencement.

There are two options for changing your student visa to one with permission to work.

HOW TO OBTAIN PERMISSION TO WORK ONCE YOU COMPLETE COURSE REQUIREMENTS AND ARE ELIGIBLE FOR THE AWARD OF A DEGREE, DIPLOMA OR TRADE QUALIFICATION

Please refer to APPLYING FOR PERMANENT RESIDENCE AFTER COMPLETING STUDIES IN AUSTRALIA in our Immigration Section of this web site.

You will note there are only certain circumstances where students may be eligible to lodge an application for migration on completion of course requirements.

To be eligible for the work experience waiver, allowing students to lodge permanent residence applications without having to evidence recent work experience, an application for permanent residence must be lodged within six months of completing course requirements. Note: This does not mean date of graduation ceremony it means the date the university considers you are eligible for the award for which you have been studying.

The primary criterion for lodging an application onshore for permanent residence on skilled grounds is to have your qualifications assessed as suitable by the relevant assessing authority.

Until recently it was necessary to have your qualifications assessed as suitable before being eligible to lodge an application for permanent residence. However you are now able to lodge your application for assessment with the relevant assessing authority and submit a receipt from them together with your permanent residence application. This means it is possible to lodge an application for permanent residence as soon as you receive your academic transcript and letter of completion from the educational institution together with the receipt from the assessing authority.