Too big images and tables can make the guideline scroll sideways, or they are resized and that might in some cases be not proportional.
If you want an image or a table to scale with current screen size of readers, you need to set the size of the image or table to a percentage. You can set it to 100% (always cover whole width) or e.g 80%.
You do this by right-clicking on the image or table and choose properties. In the size setting you write your wanted percentage in the width box, and nothing in the Hight box (it will auto-scale).
In properties you can also choose borders, alignments and so on.
If you do not want your table to divide when there is a page break you need to go into the Table properties, and write in "page-break-inside:avoid" in the Style input box in advanced settings (see image below). If there is text in that box already, like "Width:100%", you need put your text after that, and put a semi-colon between, like: Width:100%;page-break-inside:avoid"