Determine which student visa you qualify for. This depends on your Assessment Level--one to five, with five being the highest--which is determined by your home country and your area of study. The options for area of study are an English language course; primary or secondary school; vocational education and training; higher education; postgraduate research; nonaward; and AusAID and defense. Go to www.immi.gov.au/students/students/chooser/, which will help you determine for which student visa you qualify.
Check if you are a student who will need a guardian to accompany you in Australia. If you are under 18 years old you may need a guardian while studying abroad, but check with your individual educational institution for guidelines. Guardians of students studying abroad who need their guidance can also apply for a visa under the category of "student visa," since they are responsible for a student who is in fact studying abroad.
Go online to : "immi.gov.au/search/search.cgi?collection=forms_booklets&form=simple&query=student+visa&num_ranks=20&scope=%2Fallforms%2Fpdf%2F&Search=Go, a site that will help guide you through the steps of an online application for a student visa.