Well, you have to think that this is actually what we do when we are still babies. No one tell us "this is right" or "that's wrong". we just learn form our parents and people around us the way we finally speak, and that is by the way one of causes of having different dialects within the same country (it happens in every country). The main advantage of having English (for instance) as a second language is that you can actually choose the accent that you like the most.
May I recommend you watching some movies in English and try to imitate some interesting character/s and the way they speak. Also, I strongly recommend isolating the sounds of every word, as in English there are many vowels that don't exist in other languages. Don't try to learn many words, just try to learn a few words in one week and repeat them as many times as necessary until you say them without your original accent and with the right pronunciation. After that, all other words will be easier because you will already have most of the sounds in your head.
I have studied for some time different guys in Youtube where you can learn the right pronunciation of the vowels and some words where you don't pronounce every single letter (typical). Try a guy called Papa Teach Me.
Yes, you listen carefully to the pronunciation and intonation, and then try to reproduce it yourself. If you want to speak as clearly and authentically as possible, this is the best way to learn.
However, because there are various different English accents, you should choose one you like, and in which there is a lot of material to listen to, and stick to that one.