Authority: Does the author have subject expertise or special experience pertinent to the subject?
Accuracy: Is the information accurate?
Objectivity: Is the information free of explicit or implicit biases or prejudices?
Quality of writing: is the narrative clear and easy to follow?
Audience: Who is the intended audience?
Also consider:
Institutional affiliation: (for websites) Created or maintained by scholarly societies, research institutes, or governmental organizations?
Currency: (for websites) Updated or revised in a timely manner?
Organization: (for websites) Easy to navigate?