Table manners are so key that there exists a phrase, "You can tell how they were raised by how they use their chopsticks."
When it comes to Japanese food, which is registered as an Intangible Cultural Heritage, there are many particular pieces of etiquette to follow, and you'll find yourself making many faux pas in a restaurant if you aren't aware of them.
This article will go over particularly difficult Japanese manners for foreigners, with convenient pictures for easy understanding!
Be sure to give this a read before your meals at fancy Kaiseki restaurants!

First, sit down on your knees in front of the sliding screen door, called "fusuma." Use the hand closest to the door handle to slide the door open around 5cm, place your hand along the gap you've created, and open the door to about halfway across your body.

Now using the opposite hand, open the door to the full width of your body. Bow slightly with both hands, stand up, and enter the room leading with the leg on the side of the lower seats.

Do not step on the threshold or edges of the tatami mats when entering the room. This is because it is said that kami, Shinto gods, live in the threshold, so stepping on a kami leads to your family not prospering.

After you've entered the room, turn to face the sliding door and once again take a seat on your knees. Grip the edge of the door with the hand closest to the door and close it to halfway across your body.

Switch hands, and continue sliding the door closed until it's left open about 5cm. Finally, pull the door closed the rest of the way using the handle.

It's bad manners to open or close a sliding door all at once. Being careful to gently open and close the door in short intervals is very important.

Take the towel, known as "oshibori," with your right hand and transfer it to your left hand. Carefully unfold the towel, wipe both hands, re-fold so that the used portion is facing inwards, and place it back in its original position.

These towels are meant for wiping your hands, so wiping down anywhere else, such as your face or body, is bad manners. Of course, wiping your mouth while you're eating is also taboo.

While you may be tempted to use the towel to clean up the table or wipe up residual water from your drink, this is also taboo. It is a hand towel, not a wipecloth.

Turning chopsticks around and taking pieces of food using the grip-ends of the chopsticks.

Eating by spearing food with chopsticks.

Using chopsticks to bring bowls closer to you.

Wavering about above the dish trying to choose which piece to take.

Passing food from the chopsticks of one person to the chopsticks of another.

Mixing up the contents of a dish as you look for what you want to eat.

Take the bowl, lift it with both hands, and then rest it in your left hand.

Pick up your chopsticks with your right hand and tuck them between your left hand's fingers.

Return the chopsticks to your right hand, holding them properly now, and release them with your left hand.

Hold the edge of the bowl with your left hand, and gently lift the lid with your right hand.

Allow the condensation on the lid to fall back into the bowl, then finish opening.

Turn over the lid with your left hand, and place it on the right side if the bowl is on your right, left side if the bowl is on your left.