How do you roll your R's in Spanish?

Answer 1

This is one of the hardest aspects of the language to nail down! The trill of the "r" in Spanish is simply your tongue touching the roof of your mouth. To practice, pay attention to words that have a "d" sound in them. (credit, middle, word). Notice that your tongue touches the roof of your mouth. 

For the trill, you just have to keep it there a little longer, letting it bounce up and down. You may look silly, but practice Spanish trilling very much on purpose by yourself, (words like perro, carro). Let your tongue flap back and forth quickly, and just keep practicing! 

Answer 2

I agree with this expert. The tongue should touch to roof of your palate and it goes up and down a little.

Also, it takes practice... As much as you practice the better it gets. Words like "martes" , "perder", "comer", "sonar", "carrera" , "madera", can help you practice by yourself.

Please note that when there is a double RR, like "perro" it sounds like in ROPE, or ROCK in English