A quick glance at the website address can give you some clues about the website and its publisher.
For example: http://www.cdc.gov/parents/children/
Host site: CDC = Centers for Disease Control
URL extension: .gov = US governmental body
.edu = educational institution
Assessing the Quality of Health Information on the Internet
The CRAAP Test [pdf] (Californiat State University Chico)
Evaluating Health Websites (National Networks of Libraries of Medicine, NLM)
Try out your skills on these websites
Check the About Us page on websites to find out more about who publishes the website, their purpose, funding, etc.