Does this source omit facts or details?
Is it spin? Does it have a call to action?
Is it trying to sell you something? Sell you on something? Convince you of something?
If you said yes to any of the above questions, it's time to call that information into question. How do you do that?
You've heard there's a difference between scholarly and popularly sources. Check out this sock puppet theatre video to give you an idea of the difference.
Scholarly Sources vs Popular Sources from Kimbel Library on Vimeo.
That's not all though. Don't forget to think about who wrote the articles and who they are written for. Scholarly articles are written by...wait for it...scholars. And by scholars, we mean professors, researchers, and scientists: people who are experts in their fields. So who writes popular articles? For the most part it's journalists, whose expertise is usually writing, not the content area they are writing about.
As for audience, scholarly articles are written for other experts in the field and students in those areas. This means you'll sometimes get words or specialized terms that you may not know. Don't be afraid to look them up. Popular sources are written for everyone, so you get generalized language that might be a bit less specific.
No checklist will ever substitute for good old-fashioned thinking about your sources, but here are some to get your brain started down that road.