Online documents make it very easy to cut and paste information without thinking and without giving proper credit. Make sure you understand how to cite your sources. The OWL at Purdue is an excellent online resource to help you cite properly. Click here for the MLA style link at OWL. Also visit the library's free citation tool page.
When it is time to gather all of your notes and start writing the paper, avoid the most common mistake - plagiarism. Plagiarism is not only taking large parts of someone else's work and not attributing credit to that author; paraphrasing sections of a work, even using synonyms and citing the work, is also plagiarism.
Even if the ideas are rewritten, the source of the idea must be cited and the author given credit.
For further information, see the material on paraphrasing from the OWL at Purdue.