The very first thing you have to do is to create a Facebook application.
There a useful tool that checks how Facebook sees your page: https://developers.facebook.com/tools/debug
For example, checking a News object on a Plone website, this what you can get.
Please, note all of those 'og:xxx' properties that has to be added to a standard Plone page.
There is also a warning about the image loaded in that news. It's about the fact that the usual image_mini is 140x200 and Facebook wants to have at least one 200x200 image set on the 'og:image' property.
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