In the wake of the brouhaha over police affidavits (causing the state government to rush through legislation to retrospectively validate their search warrant applications, discussed here) it's probably timely for everyone who witnesses documents to reacquaint themselves with the formalities.
I don't know how much time law schools spend on this issue these days, but I'm prepared to bet it's not much - which is probably a mistake, given how much time a junior lawyer spends in the preparation of affidavits, and how important the correct procedure can be.
This brochure from the Department of Justice is an easy read:
Honorary Justice Office - Guidelines for Authorised Witnesses
The most common mistake I frequently see being made (other than a witness failing to legibly state their qualification for receiving affidavits or witnessing statutory declarations) is a corporation purporting to swear an affidavit, rather than having an officer of the corporation swear it on behalf of the company.