Q. How do you pronounce the Japanese "r"?
A. The Japanese "r" is different from the English "r". The sound is sort of between the English "r" and "l". To make "r" sound, start to say "l", but make your tongue stop short of the roof of your mouth, almost in the English "d" position. It is more like the Spanish "r".
The Japanese have trouble to pronounce and tell the difference between the English "r" and "l' because these sounds don't exist in Japanese.
Don't get too frustrated trying to pronounce it right. When you say words, there is no point in focusing on one syllable. Please listen carefully to how a native speaker pronounces it and repeat it the way you hear it.
If you can't manage it, "l" is better option than English "r", because the Japanese don't roll their tongue when speaking.
Click this link to hear the Japanese "r" pronunciation.