Start in time. Beginning early gives you enough time to properly research and write your paper. Further, not procrastinating lets you ask questions about citations and get help. If you start early, you and your instructor can catch errors; this is important because some writing errors can land you in trouble.
Take careful research notes. Most writers use their notes to write their rough drafts. But if they take rushed or sloppy notes, they can mistakenly blur the writer's language with the book or interviewee's' language (see references 1). Such a mistake often leads to plagiarism. Hence, create a method to distinguish your language from the book or interview's language (see references 1). You can color code it, enclose copied text in quotation marks or write your notes and the author's language on two different pages.
Close the book or look away when paraphrasing. Plagiarism can happen when you use language that too similar to the author's while paraphrasing. Purdue's Online Writing Lab recommends relying solely on your notes and memory as you paraphrase. (see references 1)
Cite when in doubt. Always err on the side of caution if you're unsure about whether you should cite (see references 2). According to a Princeton University article titled "When to Cite Sources," you'll never get into "trouble if you acknowledge a source when it's not absolutely necessary." (see references 2)