Employing a child's language learning style is not feasible for an adult. It is not possible to re-train your ear to hear as a child does, so understand that adults must employ different language learning strategies. Children try different words and sounds over and over again until they get what they want. Adults do not often have the time or patience to learn using this method. Some experts even believe that, as the brain gets older, we loose the ability to make new connections and learn new ways to hear language. If this is true, it would make it fundamentally impossible to learn a new language as a child would because the wiring is there to hear and speak as an adult with the language you first heard when you were a child.
Adults can, however, readily learn new language rules. So, if you are beginning as an adult, start with listening, guessing, trying out new sounds and pronunciation. Learn the rules of pronunciation along with explanations of what to do with your mouth and how sounds change based on tongue positions. It may help to begin with a tape-recorder to hear yourself and then compare that with pre-recorded native speakers. This will help over time as you train your ear and your mouth to work together to pronounce words in new ways. Children should take the same approach, but the desired result may be achieved much more quickly than for an adult.
Work on improving your prosody, rather than individual sounds. Prosody is the larger patterns of a language, like rhythm, tone/intonation, and pausing. Prosody can vary from language to language, and in English, prosody is used to convey emotion. For example, the phrase, "Leave me alone," has a different meaning when accent is placed on the final word, such as, "Leave me ALONE." In this way, native speakers add nuances to a language that those who are not native may not hear, let alone be able to mimic or intuit.
Know that accent reduction is a long process. It's very rare to loose an accent entirely if you spoke only your native language up until puberty. The brain is hard-wired to learn and adjust sounds until about 12 to 14 years of age after which it becomes more difficult to alter the speech patterns and sound recognition. Do not be discouraged by this information, rather set reasonable goals for yourself and understand that losing an accent entirely isn't necessary to gain the benefits of accent reduction.