Selecting and evaluating sources is about credibility - the credibility of the authors of the sources and your own credibility. Consider the quality of the source, whether the author is trustworthy on that topic, and what the source offers (does it offer facts? an opinion? a new idea?).
Not sure which sources are best? View this Evaluating Sources for Credibility video.
When integrating sources into your own work, you want to:
"In most cases, your best bet is to know your material well enough that you can set a source aside and write about its ideas in your own words. Otherwise, you run the risk of simply compiling a data dump or creating a patchwork of quotations. When you can sum up the gist of a source - its main point - instead of quoting from it excessively, that will save your reader time and will demonstrate that you really know the material. It will also leave more room for you to put your own stamp on the ideas you are writing about." From Getting Started - a Guide to How the Library Works: Using Sources.
Publication Manual of the American Psychological Association by See our Citing Sources Guide!
Zotero is a "powerful, easy-to-use research tool that helps you gather, organize, and analyze sources and then share the results of your research". Works within your browser and is excellent for extensive projects or managing multiple research topics.