Tell me if this link is not appropriate, but since Ashton Kutcher helped fund Duolingo, I thought it might be. This is aimed at teens (a good proportion of Duolingo users, I assume), but good tips for us oldies, too! His advice to be "smart, thoughtful and generous" is certainly behind the concept of Duolingo. http://www.upworthy.com/ashton-kutcher-just-told-a-bunch-of-teenagers-how-to-be-sexy-in-the-smartest-way-ever-3