Question 1: The key is usually long hours in a language lab where you hear words and phrases, repeat them and then listen to yourself. This, along with class, works well enough for most people.

Some people cannot, at first, hear certain sounds in a new language. Usually a language teacher makes them aware of these sounds. If that fails, one could hire a phonetician (like Henry Higgins in the movie "My Fair Lady"), a linguist skilled in the way one shapes ones vocal apparatus to make sounds in a particular language or languages. Some language textbooks provide descriptions of how to do this.

Question 2: A language lab.

https://en.wikipedia.org/wiki/My_Fair_Lady