Pronunciation is always a difficult skill, but you don't have to sound like a native speaker to be fluent. Make your goal communication, so that a native speaker can understand and have a conversation with you.
To speak clearly, practice more than the sounds of words. Intonation and rhythm are equally important. I often ask my students to listen to short passages, and then repeat, repeat, repeat aloud. I do this both in the class and as assigned homework. I also ask each student to record his/her voice of the same passage for comparison, and to slowly work towards improved clarity.
It's a long process that's hard to measure. But remember: You don't have to sound perfect to have a real conversation with someone in English.
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