First of all, if you are currently planning to eat an omakase sushi course, or will be doing so soon, you do not need to worry about this at all. The restaurant should serve the day's recommended toppings in the order they think is best.
On the other hand, when you go to a conveyor-belt sushi shop or a restaurant where you order à la carte, what order should you eat the toppings in? Is there some rule?
There are many opinions, but in the end, many people seem to say that everyone should simply eat the toppings they want in whatever order they like.
If you want a small point of reference on that basis, there is also the idea of starting with mild white fish and moving toward richer flavours. This is because strong-tasting toppings or fatty pieces such as toro are said to blur the taste of the next topping. However, another view says that after a strongly flavoured topping, it is enough to refresh your palate with hot tea and gari.
As a side note, sushi is also something for enjoying delicate flavours and aromas, so restaurants that allow smoking are generally rare, and wearing strong perfume is not considered very welcome.
