Play a single melody using both hands. Imagine a harpist's performance, moving gracefully, and playing with well-aligned notes. The notes played by the left hand tend to become too loud. I believe it is effective to practice by smoothly singing each phrase and then playing, using that singing as a model. Furthermore, the last note of the slur is an eighth note. This seems like a message from the composer, asking for careful playing. The right hand plays third intervals with fingers 5-3-2-1 respectively. Try practicing rhythms, etc., so that you can move freely and smoothly in both ascending and descending passages.