A few things to keep in mind when looking for and working with primary sources:
Context - In what context was the creator of this source working? What might have influenced them? For example, if you've found one good newspaper article, what was on the cover of the newspaper that day? What were the advertisements? If you're reading blog posts, what other posts does the blogger link to?
Audience - Who is the intended audience for this source?
Format - Consider how the format you've found the document in might impact your assessment and analysis.
A scanned image of a document illustrates what the original document looked like (including handwriting, marginalia, etc.). This might give you a different perspective on the document than a transcription, in which the document is reduced to its text.
Primary sources are firsthand accounts of events or conditions during a particular period, often recorded contemporaneously by participants or observers.