In order to pronounce rr correctly you should let the tip of the vibrate. Practice with words like perro, perra, Tarragona, barra, etc. Try to do it over and over again. The French, Germans and Chinese have a hard time pronouncing this. English speakers tend to slur the rr.

This article can help you... http://spanish.about.com/cs/pronunciation/ht/rr.htm .. And I hope you can understand this video ..it is cantonese language: Alveolar Trill (Rolling R) explained in Cantonese http://www.youtube.com/watch?v=SDVWogLNRMI&feature=related Saludos Pepe