Obtain an English study course pack, including a CD or online program that will allow you to listen to the exercises you will do in the book. The course pack should come with listening and speaking drills to help you acquire the correct pronunciation.
Record yourself as you work on the audio exercises and compare them to the accent of the native speaker from your CD. Work on any sounds you have trouble with by practicing until they become natural. "TH" can be difficult for some non-native speakers to master. Place your tongue behind your teeth and open your jaw slightly when making the "TH" sound.
Watch American movies and television to work on your listening and vocabulary. You can begin by watching the movie with English subtitles the first few times if you have a hard time following the dialogue, and then watch the movie without any subtitles.
Study and practice reading, speaking, listening and writing English every day. Even if you only study for 30 minutes a day, it will help you to continue building on what you have learned to gradual improve your ability. If you miss a few days of study, you will have to review what you have forgotten and you will waste time and fall further behind in your study.