Are you fairly fluent, but still struggle to pronounce certain words correctly? Many people who speak English as their second or third language have an enormous vocabulary, but still have trouble pronouncing the words correctly.
That might be due to several reasons. Firstly, remember that there is a difference between having an accent and saying words wrong. There are many places in the world that speak English as a native tongue, but each of those places have different accents and their own unique dialects. Even within one country, say for example England, people living in certain areas sound completely different to people in other areas. That doesn't mean any particular group of people are wrong or pronouncing words incorrectly.
However, in the English language, words have certain syllables that should be emphasized, some letters are silent and therefore not said at all, and some groups of letters together create a different sound than that of the individual letters, or might just sound slightly different from one word to the next (take for example the words "cat" and "car", where the letter "a" has a different sound in each).
If you find yourself saying words not quite as they should be said, your ear might still be a little untrained. If you don't hear native English a lot, it might be harder for you to know how to say certain words. A good tip is to watch a lot of English movies or series with your preferred accent, whether it's American, British, Australian or anything else. Try to repeat certain words and phrases until you sound more natural.
The other thing you can do is to interact with a native speaker on a daily basis. Chatting to a friend or tutor regularly will help you get used to certain sounds and you will find yourself adopting their way of speaking.
I hope you are encouraged and remember, practice makes perfect!