BBC Learning English is a great website for students of English. As far as pronunciation is concerned, they have a guide to phonetic symbols and also videos to show how to pronounce each of the sounds. There are also activities to practise identifiying the difference between certain sounds which may sound similar.
The video below is just the introduction. Follow the link to BBC Learning English and do as much practice as you think you need to improve your pronunciation. There are also interactive quizzes to test your knowledge of and help you learn about English pronunciation.