Make every visitor use the secure https:// version of your site.

1. WordPress: install a plugin like Really Simple SSL, which forces HTTPS in one click. Or set your WordPress Address and Site Address (under Settings > General) to the https:// versions.
2. Any site: add a redirect to your .htaccess file in public_html (article 147).
3. Test by visiting the http:// version — it should redirect to https://.

Important: Install your SSL certificate first (article 140), or forcing HTTPS will produce errors. Back up .htaccess before editing it.