Unless you start speaking English as a child it is almost impossible to be a native speaker but if you spend a lot of time in an English speaking country you can become extremely fluent.

One of my college professors said, "To be successful in anything, three things are required; practice, practice and practice!" To word your question as a native English speaker might word it, "How can I learn to speak English like a native English speaker?" The answer is not simple and neither is the process. You will need to make an in-depth study of native English speaking. This would include studying idioms, phrasal verbs, inflections, grammar, sentence structure, pronunciation and vocabulary. You will have to determine what kind of native English speaking you wish to emulate. There are many different kinds of English spoken throughout the world. There are even many different dialects spoken in my country. Most importantly are those three things needed to be successful: practice, practice and practice. May I suggest that it will be much easier and possibly better to just learn to understand and be understood as you converse in the language.

If you are lucky enough to learn languages easily, watch films/videos in English and talk to native speakers on a regular basis, you can become fluent. Of course, living in an English speaking country always helps, but it isn't always necessary.