Today at NELS I taught a pronunciation lesson on the sounds /l/ and /r/ which are really difficult for Japanese students to say and hear. I was so proud of them for being able to clearly pronounce both sounds by the end of the lesson.
If you want to learn how to make these sounds, and then practice them, check out this online resource:
There are actually lots and lots of videos online and some even specifically for Japanese speakers, so why not go surfing and see what you can find.
Also, if you look at the resources I gave for a previous pronunciation lesson on /f/ and/v/ here you should also be able to link to more /r/ and /l/ information.