The following are required to apply for a Subclass 491 visa.
You need to be invited to apply and must meet the following criteria
A state or territory government agency should nominate you, or an eligible relative must sponsor you
You should have a job on a relevant skilled occupation list
An appropriate skills assessment for the job at the time of the invitation;
You must have at least proficient English.
Must not have had an earlier application denied or a visa cancelled (if applying from onshore)