Most of what visitors worry about does not matter. A short list does.
This is the clearest difference from Japan and China. Rice and soup are eaten with the spoon; side dishes are picked up with chopsticks. Holding both at once, one in each hand, looks careless. And unlike in Japan, the rice bowl stays on the table — lifting it to your mouth is considered poor form.
Do not stand chopsticks upright in a bowl of rice: that is how rice is offered to the dead at a memorial rite. And do not start eating before the oldest person at the table does. Both are noticed. Beyond these, table etiquette is relaxed.
Stews and side dishes arrive in communal bowls and everyone eats from them, often with their own spoon. This is normal and not considered unhygienic, though many restaurants now provide serving spoons (앞접시 and 국자) if you ask. Asking for one is not rude.
You do not pour your own glass — someone else pours for you and you pour for them. When an older person pours for you, hold your glass with both hands. When drinking in front of someone senior, it is customary to turn your head slightly away from them. These are followed more strictly than eating rules.