Streams in most maps are going to follow something in the song such as the drum beat or synthesizer. In Mendes it's following the piano. Listen to the map with relax or auto and you should be able to hear the hitsounds matching up with it. To work on your control try to develop a mental metronome as you play through streams. For example: keeping a 1-2-3-4 rhythm in your head during average length streams.