Scan the perimeter of the page for information about the creators of the page, the purpose of the page, and when the page was last updated. Look for links such as "About Us" or "Contact Us."
If you cannot find an author or publisher for the page you can try truncating the URL. In the web address box, delete the end character of the URL stopping just before each / (leave the backslash). Then, press enter to see if you can learn more about the author or the origins/nature of the site providing the page.
Look at the domain name of websites. The domain name of the site can give you an indication of possible bias. For example, a .com is, by definition, a commercial site so they may be trying to sell you something. This is not to say that all or even most .coms are unreliable because that is certainly not true.
Pay attention to the style of the language used on the site. Is it balanced and professional with both sides of the issue covered, or does the language seem inflammatory or biased?