Facebook fetches meta data from a page when people share the link. Therefore you can add some in your page for the case.
First of all, at least add "og:title", "og:description" and "og:image" to your page. Like below:
<head>
<meta charset="utf-8">
<title>title</title>
<meta property="og:title" content="title" />
<meta property="og:description" content="the description about your page" />
<meta property="og:image" content="http://domain.com/images/logo.jpg" />
</head>
then go to http://developers.facebook.com/tools/debug and type in the url of your page to see what facebook fetched.