One aspect of Spanish pronunciation that can be tricky to master is the trilled or rolled r, which is also known as an alveolar trill /r/. This sound is also used in Italian and many other languages. Some people seem convinced that if you can’t already make this sound, it’s impossible to learn.
If you are having trouble with the Spanish r, this blog post might help. It breaks it down into a four step process and explains clearly what to do at each stage. There’s another explanation of how to make this sound here.
Once you’re got those r’s rolling, here’s a tongue twister to practise with:
Erre con Erre Cigarro
Erre con Erre Barril
Rápido corre el carro
Repleto do ferro en el ferrocarril
It is possible, in fact, to learn to make any sound used in any language, even the rolled r, and other tricky sounds like the clicks used in some African languages and the back-of-the-throat sounds of Arabic. It takes a lot of listening and practise. An understanding of the mechanics of how the sounds are produced can help as well.
There are online introductions to phonetics and phonology here and here, and this site shows you the relative positions of the tongue, teeth, lips, etc when pronouncing various sounds.
I can usually manage alveolar trills, though sometimes find the double rr in the middle of words such as carro a bit tricky and I have to slow down to get it right.