Tips to improve your spoken Spanish fluency: it involves traveling!
It is indeed every language learner's dream, be it explicit or a secret one. Speaking a foreign language just as those native speakers do is considered the hardest step in the process of acquisition. As if grammar and vocabulary were not enough, now you are faced with intonation structures, phonetic symbols, diphthongs and so much more. After enormous efforts, it seems impossible. But that is not quite the case.
First of all, why is it so hard to achieve accent-free speech? The human ear is very sensitive to the tiniest differences in pronunciation, and a native speaker will immediately sniff out a foreign accent. Even though making out the accent is very easy, mimicking how a native speaks gets increasingly difficult with age. Children, in fact, have the remarkable ability to copy their parents' speech and that is why children with parents with different native languages turn into such perfect bilinguals. They lose this ability later, though, and struggle just as monolinguals when faced with the task of removing their foreign accent.
There are, of course, people with extraordinary mimicking abilities who copy speech with incredible ease even later in life. But we will not look at that, because they are the exception.
So how can you do it? What is your best bet in this seemingly impossible task? I will introduce you to my experience.
Listen to natives as much as possible. Train your ear to distinguish the different sounds, even the tiniest ones. Try to focus not on words, but on the sounds which form them. You may need to cover some theoretic phonetics at first. You will find many details which you never even paid attention to.
Do not mix the accents you hear. In the case of English, focus on either American or British accent, as they have some very distinctive features. If you mix them, you might create a phonetic Frankenstein.
Do not shut up! Talk your heart out on your favorite topics, and find a native who will honestly and positively point you in the right direction.
In time, you will notice how your accent fades away. For many people, the best result is only a string of speech without an accent, but if you are determined, you can go further.
Do not hesitate to do it. It always impresses native speakers!