Is the information current enough for your topic? (Be sure to put currency into context. Computer science is an area that moves very quickly, so sources need to be more recent than a topic such as history.)
Has the information been revised or updated in a later publication?
Has the information since been refuted by other journals or publications?
Who maintains the website? (Is the site stable? Will you be able to access it a month from now? If the URL has changed, is a hyperlink to the new site made available?)
Are there broken links that indicate that the site is not being kept up-to-date?
Does the software used in the site present limitations?
What to look for on a webpage
Look near the top and the bottom of the webpage to see if any publication date, copyright date or "date last modified" is indicated.
Look for other indications that the page is kept current. (Is there a "What's New" section? If you are using a website with content written by different people, there may be different dates - a date for the website as a whole, and a date when the individual article/post was written.)
Check the collected date and / or published date of any statistical data or charts.
What to look for in print material
Look at the publications details at the front of a book. Has the information been revised or updated? For a journal, look on the cover or title page.