I've assembled a few web resources that you can check out to help you avoid plagiarism.

http://www.plagiarism.org/plag_article_plagiarism_faq.html
http://libweb.uoregon.edu/guides/plagiarism/students/
http://www.wadsworth.com/english_d/special_features/plagiarism/strategies.html

And this site offers a variety of pages to help you improve your writing skills:

http://www.ipl.org/div/aplus/links.htm#writing