When using Microsoft custom Master Pages, print preview pages dont show any
content in the body of the page. Reason: Sharepoint use core.css file in which they write few classes where they says that this class should not be use for print/media. Solution: While customizing make sure not to use those classes on top of your body area. So that it wont hide it. Few classes: Few of classes I m mentioning below which if you use on top of body area then print will not display content. .ms-leftareacell,.ms-globallinks,.ms-siteaction,.ms-areaseparatorleft,.ms-rightareacell,.ms-areaseparatorright, .ms-areaseparatorcorner,.ms-titlearealeft,.ms-titlearearight,.ms-searchform,.ms-banner,.ms-buttonheightwidth,.ms-buttonheightwidth2
Hope this help you.
Thanks! Avinash | 