This code will ensure that all WordPress custom post types appear in the main blog loop/query on the home page as if they were normal posts.

pre_get_posts.php

function pre_get_posts( $query ) {
	if ( $query->is_main_query() && ! $query->is_admin && $query->is_home ) {
		$post_types = get_post_types( array( 
			'public' => true,
			'publicly_queryable' => true,
			'exclude_from_search' => false,
			'show_ui' => true,
			'hierarchical' => false
			) );
			
		if ( isset( $post_types['attachment'] ) )
			unset( $post_types['attachment'] );
			
		$query->set( 'post_type', $post_types );
	}
}
add_action( 'pre_get_posts', 'pre_get_posts' );