To avoid plagiarism, one should always provide information of the sources used, i.e., you must document or cite the sources of information which you have consulted or used in writing your paper. Therefore, it is important that you keep records of all sources that you have consulted (i.e. note-taking) so that you will be able to provide proper citations later.
Most people plagiarize not because they want to act unethically, but because they do not know about the concept of plagiarism, so they plagiarize unintentionally. Below are the "Seven tips" to avoid accidental plagiarism.
Tip 1: Use your own ideas
YOUR IDEAS should always be the FOCUS of your own work.
Tip 2: Cite the sources 
When someone else's ideas are used, always acknowledge the sources and tell your reader WHERE THE IDEAS ARE FROM.
Documenting or citing sources of information involves 2 parts:
1. In-text citations - brief references within the text of the paper
2. A complete list of citations* or references at the end of the paper
Refer to the Citing Sources of Information research guides for more about how to cite sources using your required citation style.
Tip 3: Indicate clearly when copying directly from a text
When using the exact words of an author, the direct quotes should be identified by quotation marks or typed in as an indented paragraph. Show your reader exactly WHAT IS COPIED.
Tip 4: Rewrite other's ideas in your own words
Quoting, paraphrasing and summarizing are 3 ways of incorporating other people’s work into your own writing.
Quotations, as mentioned in Tip 3 above, must be identical to the original.
Paraphrasing and summarizing both involve putting other’s ideas INTO YOUR OWN WORDS.
Effective paraphrasing can help you prevent plagiarism! Refer to this guide to learn more about paraphrasing.
Tip 5: Start early
Give yourself SUFFICIENT TIME to:
Tip 6: Take careful notes 
Accidental plagiarism is often the result of bad note-taking. Do not just take notes about someone else's ideas, but also the sources of these ideas.
1. Record all details about the source of each reading to ensure proper acknowledgement in your assignment. These include title (title of journal, book and article), author's full name, publisher's name, year and place of publication and page numbers.
2. Distinguish carefully between any ideas from your reading and your own ideas to avoid copying other's ideas without acknowledgement.
3. Use quotation marks for direct quotes (i.e. author's exact words) so that you will also do so when using these notes in your assignment to avoid plagiarism.
Tip. Use CityU LibraryFind to save the details of references you consulted for your research so you can refer to this information later when you need to cite the references. Note: Remember to sign in to CityU LibraryFind.
Tip 7: Develop your writing skills 
To be able to use your own words, it is necessary to develop YOUR OWN VOICE and WRITING STYLE.
The English Language Support Services (ELSS) at CityU provides an array of workshops, services and activities to enhance your English communication skills.
Plagiarism detection systems are automatic text-matching systems to detect plagiarism. Turnitin is such a system supported and maintained CityU E-Learning Team. Instructors may ask their students to submit their assignments via Turnitin in Canvas by enabling Turnitin as part of a new Canvas assignment.
For more, refer to the E-Learning Team website: http://www.cityu.edu.hk/elearn/elearn_stud.html
There are also some sites that provide basic free plagiarism detection functionalities. Here are some examples: