Who is the author? Are qualifications or credentials listed? Is contact information provided?
Check the date for currency. Is this important for your topic? Is the information still up-to-date? Are links on the site still working?
Is the information accurate? (Compare to other sources.) Are sources cited?
What is the purpose of the site: To inform? To sell a product or service? To persuade? To entertain?
Is the information biased? Does it present different points of view?
What is the level of language: Easy enough for a child? Generally understood by an adult? Scholarly? Technical?
Check the domain: .edu – college or university, .org – organization, .gov – government agency or department, .com – business
.edu and .gov sites are regarded as consistently authoritative
.org sites are often authoritative (but be aware of bias)