Authority - what are the author's experience, credentials, or affiliations? What are their affiliations? look for sources with named authors who have the experience and knowledge
Credibility - where is the author getting their information? Do they list their sources?
Audience/Purpose - is the author speaking to a particular audience? Do they have a particular perspective, or agenda? Are they trying to sell you something?
Currency - does the website have a date? Is it maintained and updated?