Students often come to information evaluation thinking that the primary thing they should be concerned about is bias. And since everyone has some form of bias, that ultimately leads to students thinking no one can really be trusted.
Instead of bias, it's agenda that should be your primary concern for information evaluation.
Bias is about how people see things; agenda is about what a news or research organization is set up to do. Ask first and foremost when approaching an organization or source "What is this group set up to do?" Research? Political advocacy? Marketing? Their agenda is much more important in determining trustworthiness than any personal biases the writers might have.
A site that clearly marks opinion columns as opinion, employs dozens of fact-checkers, hires professional reporters, and takes care to be transparent about sources, methods, and conflicts of interest is less likely to be driven by political agenda than a site that does not do these things. And this holds true even if the reporters themselves may have personal bias. Good process and good culture goes a long way to mitigating personal bias.
The SIFT Method portion of this guide was adapted from "Check, Please!" (Caulfield). The canonical version of Check, Please! exists at http://lessons.checkplease.cc (CC-BY). As the authors of the original version have not reviewed any other copy's modifications, the text of any site not arrived at through the above link should not be sourced to the original authors.