Change a WordPress site's homepage default social meta added by the Jetpack plugin for Facebook's Open Graph and Twitter Card tags.

WP-social-meta.php

<?php
function hearvox_social_meta( $tags ) {
	if ( is_home() || is_front_page() ) {
		// Remove the default blank tags added by Jetpack
		unset( $tags['og:description'] );
		unset( $tags['og:image'] );
		unset( $tags['twitter:site'] );
		unset( $tags['og:title'] );
		unset( $tags['og:url'] );

		// Add custom tags (Twitter grabs the OG image and description)
		$tags['og:description'] = 'Short description of webpage.';
		$tags['og:image'] = esc_url( 'http://example.com/image-dir/image-filename.jog' );
		$tags['og:title'] = esc_url( 'Title of Webpage' );
		$tags['og:url'] = esc_url( 'http://example.com/' );
		$tags['twitter:card'] = 'summary';
		$tags['twitter:site'] = '@hearvox';
		$tags['twitter:title'] = 'Title of Webpage';
	}
	return $tags;
}
add_filter( 'jetpack_open_graph_tags', 'hearvox_social_meta' );
?>

Validate Facebook's Open Graph data:
https://developers.facebook.com/tools/debug/

Validate Twitter Card data:
https://cards-dev.twitter.com/validator

Jetpack info for Open Graph:
http://jetpack.me/tag/open-graph/