One key to avoiding plagiarism is to know what you need to cite and what you do not. A good rule of thumb: if in doubt, cite it. But there are some other basic principles to keep in mind.
You do not need to cite information that is widely known or easily accessible in basic reference books. So, you do not cite a source for the fact that the Declaration of Independence was written in 1776, nor do you need a page number reference for its well-known opening words (“When in the course of human events..”). But if you were to go on to discuss something more subjective, such as the colonial public’s reaction to its publishing, you would need to cite your sources.
Many students are reluctant to cite study aids (CliffsNotes, SparkNotes), online reference tools (Wikipedia), and other websites and blogs. This attitude is understandable if you are trying to conceal from your instructor that you have used such resources, but be aware that such deception leads to plagiarism. Any resources you use to spark your imagination or inspire you must be cited even if you are embarrassed to have used them. It is not enough simply to include websites in a bibliography; the body of your text must indicate clearly what ideas are from the resource and how your own thinking was affected by those ideas. Students sometimes say that they cannot remember which ideas they had before they started reading and which were suggested by the resources themselves, but this excuse will not do. A responsible writer keeps track of such things and represents the source of ideas accurately in the work.
But more importantly, be aware that your instructors actually value the ability to use resources for inspiration responsibly. Your paper will be well-received if you demonstrate that you are able to use the ideas of others to develop new ideas. You therefore strengthen, not weaken, your paper by visibly incorporating your sources. One suggestion for doing this well: rather than reporting the ideas of the sources as simply true, use contrastive words to link your ideas to those of your sources while simultaneously showing where your thinking has advanced. Consider the constructions of the following:
Beowulf can be classified as an epic poem because of its length and its status as an early work in the language (Wikipedia); however, we might ask whether this category is in fact a good fit for this folkloric tale.
There has been some question whether Davy Crockett died in action at the Alamo or was executed after being captured. Discussion of this question by amateur historians on an Alamo enthusiast’s website offers no credible conclusions (The Alamo Site), but does suggest that what is at stake is less what “really” happened and more about our popular definition of bravery.
Using popular resources like Wikipedia and blogs on the internet can be fine as long as they are properly cited, and as long as they are not confused with authoritative academic resources.