Use a style that has the paragraph formatting of "Page Break Before."
I will usually set this as the setting for the Heading 1 style. Apply that style to the paragraph/heading you want to begin a new page.

• Importance of Styles in Word
• Why Use Word's Built-In Heading Styles? by Shauna Kelly
• Word Doesn't Know What a Page Is by Daiya Mitchell, MVP
• For more: Basic Concepts of Microsoft Word - from Shauna Kelly