If English is your second language and you're just starting out, you can improve by enrolling in an English class. Practice frequently, and speak the language at every opportunity. If you really want to take it to the perfection level, you can take an accent reduction course.
Listen to music in English, translate what lyrics you can, then look up the ones you don't. I know for Spanish, I had to listen to the same songs repeatedly before I could clearly hear the words I knew were being said. Also, read. The more you read, the more you'll begin to pick up on the weird parts of English that shouldn't make sense grammatically but do. Use a thesaurus to broaden your vocabulary.