If you know *why* an article was written or a website was created, that goes a long way to helping you evaluate it as a reasonable source. Here are some things to consider:
What is the purpose of the information?
To inform? teach? sell? entertain? persuade? Which of these might be most valuable to you as s source? Do you think a website trying to sell you nutritional products might "spin" their argument in favor of what they sell? If an article is trying to teach you something about black holes, might that be more believable?
Do the authors/sponsors make their intentions or purpose clear?
In other words, (going back to Authority) do you know who the author or website creator is? If you can't figure that out, be wary.
Is the information fact? opinion? propaganda?
This is important. Not everything you read on the internet is true. Not everything you read in an article is true. Analyzing arguments will help you understand this point even better, but you must be able to differentiate fact from opinion.
Some sources are trying to tell you what is true. Other sources may be trying to persuade you that something is true.
Honest sources will let you know they're trying to persuade you, like opinion pages of a newspaper.
Less honest sources will try to mask their persuasion. Watch out for those sneaky ones!
Does the point of view appear objective and impartial?
Think about it this way: Is the source on a controversial topic? Does it reflect different sides of that argument? Does it represent all sides equally?
Is there political, ideological, cultural, or religious favoritism?
Is the source trying to score points against "another side"? (This goes hand in hand with being objective and impartial!)