There are a number of criteria to take into consideration as you evaluate resources.
Purpose - Why was this item written?
Authority - Who wrote it, what are their credentials?
Currency - When was the item written, does currency matter? It may not depending on your topic.
Accuracy - This can be hard if you don't know much about the topic. Generally books and articles go through some type of editorial process. Does the resource have references you could check?
Relevance or content - Does the resource address your topic question?
Audience - Who is the intended audience?
In addition, there are some specific things you can look for when evaluating a website:
Look at the end of the url (uniform resource locator) Is it .org, .com, .edu or .gov?
.org - nonprofit organizations
.com - commercial/business
.edu - university or college
.gov - government site
Look for an "About Us" link or something similar. This often gives you information about the website.
Review the diagram which explains the Invisible Web and pay particular attention to the types of websites and information Google can NOT access.