There is an English sound which is used more than any other. The trouble is it’s a short sound which can be very difficult to hear as it is only present in unstressed syllables.
Pronouncing this sound correctly and in the right place really helps to get a natural flow to spoken English. Helen has more information in the video.
For a summary and an exercise: https://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-10/session-4