Something about the pronunciation
Each Spainish learner konws that there is a "Rolling 'R' ",I can do it well when I am only rolling my tongue.But in the words,I cannot do it as well as I do it singly.How can I improve this pronunciation?
Just talk as much as possible. The more you do, the less you focus on sounds that are unfamiliar (because they begin to become more familiar). When that happens, you relax instead of working yourself up to pronouncing it.
I had alot of difficulty with the Arabic 'ain sound. I really don't anymore, because I've been using it so much that I don't really think "oh no! an 'ain is coming up" any more.
The trick for me was adjusting where and how I was doing the R. This has some tips that might help. Be sure to watch the videos!
FWIW, one of my Spanish teachers said that it's not common for adults to learn to trill the rr. Even some native speakers (particularly in Puerto Rico and Mexico, IRCC) can't trill, and it's not a big deal.
Okay, this is going to sound silly but a friend from Germany told me that he learned how to do it when he was imitating his cat. When they do that ''prrrrr'' sound, you know? And then, without stopping, he would pronounce ''prrrrrRojo'' or ''prrrrrrRosa''. I don't know, maybe it helps you.