Watch this TED talk by Eli Pari­ser.  As usu­al try to under­stand the spea­ker WITHOUT subtitles.

Now ima­gi­ne that you want to tell a friend / class­ma­te about this video. Simu­la­te this talk. Now stu­dy the tran­script.  Final­ly prac­ti­se / impro­ve your talk again.