Since the ancient time, Japanese think that the left side is superior. For example, in Japan, they wear their traditional clothing, kimono, with the left side wrapped over the right side .
The reason why rice comes to the left is that Japan has treated rice with respect since rice cultivation was introduced in the Yayoi period（10th century BC – mid-3rd century BC）.
Rice, which has also been deified, is not just food for Japanese people, but it is a precious being. So rice is served and placed on the upper left side.
The location of miso soup is on the right, because miso soup iss a side dish of rice.
The similar manner is also practiced for sushi serving in which miso soup is placed on the right side of the sushi. Put the lifted things back in the same place.
Don’t lift Sushi geta(sushi plate).
If you are interested in Sushi culture, I recommend SUSHIDO with sushi (We also have vegetarian menu) when you visit to Tokyo.
If you are interested in Shitamachi(Do you know Shitamachi?) ,secret spots in Tokyo and Japanese casual conversation for trip, I recommend Online Japanese lesson.