First of all, there is no easy fix and it does require a great deal of motivation and hard work.
As a pronunciation coach, I see the pain and struggle that my students usually experience before they could find concrete results.
The answer to your question depends on several factors such as your age, musical ear, motivation, passion, patience and practice.
Let's look at each one of these factors:
Age: The older you are, the harder (not impossible) it gets.
Musical ear: Do you have a musical ear? Are you naturally able to distinguish between one sound and the other? Can you pick up small sound nuances in language?
Motivation: What do you need it for? Do you need it for work? for career?
Passion: How much do you love it How much do you want it? If you don't love it, you'd soon give up.
Patience: It does take a while to build a muscle memory and reprogram your brain to easily and effortlessly produce and recognize a new set of sounds. You have to be patient, otherwise, again, you'll end up giving up before you even start.
Practice: I guess this one answers your question directly. Just like any other physical skill, speaking clearly, naturally and without the influence of your native language on English truly needs plenty of training and practice. You ought to spend ample of time
- repeating, recording, self-monitoring, self-assessing, recording again.
- Listening to native speakers while sometimes watching their mouth movements. Also pay attention to their voice patterns.
- Learn the IPA (International Phonetic Alphabet) and research the common pronunciation problems that learners who speak your native language have. I am more than happy to give you a handy list of those common pronunciation issues if you tell me a little bit more about your linguistic background.
- Listen to rap songs. Yes believe it or not, they are wonderful tools for English learners to use to improve their listening and pronunciation. Don't just listen to them, but also try to follow them, which, needless to say, you won't be able to do, but it doesn't matter as the point is that you are training your ears and mouth to move differently.
- Use tongue twisters. Depending on your pronunciation problems, you can choose a number of tongue twisters to help you target these problems and there are hundreds of them on the net. That is going to be difficult as you probably won't have anyone to correct you, so you're going to have to rely on your ears and again record yourself and monitor your own performance.
It is all about practice, practice and practice. If you do not have the time to practice, it won't happen. If you don't have the musical ear, then you need a pronunciation coach to guide you, monitor you, correct you and give you feedback.
Feel free to read my article "6 tips to take your English to the next level" by clicking on the following link 6 Tips to Take Your English to the Next Level | ENGLISH Speak Like A Native.