1. Read about word stress (and the sound "schwa"), then also about sentence stress - this can be an eye-opener! :)
2. Watch videos about reductions - you can start here:
3. Google "accent reduction", especially pages that explain interference from your first language so you know what to watch out for.
4. Listen to and imitate native speakers (using videos, songs, etc.). It's best if you can read the transcription of what the person is saying (or the lyrics to the song you're listening to).
Good luck! :)