Use the full list of Open Graph Meta Tags:
- og:title – The title of the entity.
- og:type – The type of entity. You must select a type from the list of Open Graph types.
- og:image – The URL to an image that represents the entity. Images must be at least 50 pixels by 50 pixels. Square images work best, but you are allowed to use images up to three times as wide as they are tall.
- og:url – The canonical, permanent URL of the page representing the entity. When you use Open Graph tags, the Like button posts a link to the og:url instead of the URL in the Like button code.
- og:site_name – A human-readable name for your site, e.g., “IMDb”.
- fb:admins or fb:app_id – A comma-separated list of either the Facebook IDs of page administrators or a Facebook Platform application ID. At a minimum, include only your own Facebook ID.
Also use absolute URLs instead of relative!
EDIT:
Please note that Facebook caches webpages for specific periods so you may not notice your changes right away. A good way to check if Facebook is/will actually take your changes is by faking a parameter in your URL.
for example if your URL reads: http://example.com/index.php
Add something like: http://example.com/index.php?123 and then use it in the URL Linter. 😉
EDIT 2:
You could directly use the Facebook Linter (now called Debugger), but be aware that some data cannot be changed in some cases, described here:
Editing Meta Tags
You can update the attributes of your page by updating your page’s
tags. Note that og:title and og:type are only editable
initially – after your page receives 50 likes the title becomes fixed,
and after your page receives 10,000 likes the type becomes fixed.
These properties are fixed to avoid surprising users who have liked
the page already. Changing the title or type tags after these limits
are reached does nothing, your page retains the original title and
type.