Few tips on pronounciation for non-native English speakers.

You should focus on aspirating key consonant sounds and stretching certain vowel sound. Place your hand in front of your mouth while saying the P, K and T sounds. You should feel a gush of air on your hand while saying these sounds. If you don't, you are not releasing enough air. These are aspirated sounds and lots of air should be used.

For vowel sounds, it is important that we emphasise and stretch them when required. For instance, the word 'bed' does not require that you stretch the vowel sound 'e'.

The word 'bead', however, does require the vowel sound to be stretched. If the lengths of the words 'bed' and 'bead' are the same when you speak, you know you are not stretching certain longer vowel sounds enough.

It is not a good idea to use a false accent while speaking.

Instead:
1. Concentrate only on your aspirated consonant sounds (p, k, t, f, s)
2. Make sure your tongue does not reach too far back in your mouth for the t, d, l, n sounds.

via Rediff

Personally I benefitted from watching English movies and serials.