You need to work with a native speaker who can give you feedback. Learners don't often realise that they are mispronouncing words.
After you've identified the problem words, it helps a lot to group those words with other words that have a similar sound. For example, a typical learner problem is pronouncing want and won't (will not) the same way, whereas they sound clearly different to native speakers. So you find other words that have a similar vowel as in want, and another group of words that have a similar vowel as in won't.
You can look up "minimal pairs" to find out more.
I was taught early on in my Turkish learning to aim for the main stress in longer words and phrases. This also helped me with Russian words and I use it with my students in English class.
Sometimes I repeat after hearing the vocabulary. Let's say that I'm watching a movie or any related, I try to repeat it and imitate it. I also write and speak at the same time, which is very helpful. Another way could be recording myself.