Find Taisho(Sushi restaurant's head chef)
When you go to traditional sushi bars or restaurants. Usually it's pretty small and there is a counter bar.
Find Taisho(Sushi bar / restaurant's head chef) and order "omakase"
Omakase means "chef's special".
They offer you today's recommendation fresh fishes. ( 12 ~15 pieces usually)
Traditional Sushi bar don't show the price so better to ask sushi chef when you order.