When reading a PDF document in Preview, you may have discovered how hard it is to hand-adjust a page's zoom and contents to provide a page-at-a-time display. The screenshot to the right shows how there's almost always either clipping or a bit of the next page to worry about.
Don't work so hard to manipulate your window. Use a few handy built-in features to better improve your reading experience.
Show just one page. Select View > Single Page (Command-2) to show just one page, perfectly centered, at a time. You can return to continuous scroll at any time by selecting the View > Continuous Scroll (Command-1) option.
Zoom each page to fit the window. Enable View > Zoom to Fit (Command-9) to ensure that the page expands as much as possible to fit the current window size. Now, instead of using the zoom-in and zoom-out options, you can just resize the window and the page size will follow suit.
View a page-by-page table of contents. For quick page navigation, enable an in-window contents display by selecting View > Thumbnails (Command-Option-2). A column of previews appears to the side of the page letting you move to the exact location you wish.
The first and third of these features are also available directly from the View pop-up that appears by default at the left of the window's toolbar. The location of this feature, which looks like a rectangle with a line and two dots on the left, may vary on your specific installation because Preview allows you to customize the toolbar.