Be sure to see if the author's credentials are specified and if not, research that person (you can usually google them). The same should be done for a publisher of a website.
Ask yourself: Is this person an authority on this subject? If not, are they citing voices who have authority?
Is the publisher reputable?
Bias
Ask yourself: Is the purpose of this site's information to inform, teach, sell, entertain, or persuade?
In what context would this source be useful?
Currency
Determine if the source is up to date
The publication date or date last updated should be displayed
Consult at least one or two other sources yourself