Defending in JK2 is at the core just to point your saber towards the opponent's attack. The safest option is of course to stay out of reach.
There is a zone at the front of your body where your character will block attacks, whether they are swung at your feet or head. This can be done in any state when not attacking - running, walking, jumping, crouching, even rolling.
When attacks start coming in from the sides, you will get hit unless you turn to face their point. So keep your saber between you and your opponent at all times, whether you are attacking or just guarding. The more blade they must cross to reach you, the harder it will be to get around your block. Therefore, looking a bit downward, laying the saber more horizontally when blocking is good practice. Another reason is that you will direct your point at them, making it harder for them to riposte with red stance. You can read more about that here .
There is another more advanced way to block attacks, by intersecting , and it belongs to the advanced section. However, the principle is the same - even when you attack, keep your opponent's saber from reaching your body.
An extension of intersection, but which is worth talking about separately, is coverage. Coverage is when a swing closes a line, both during and after an attack. One of the most fundamental concepts of sword fighting is to protect against the afterblow - most opponents won't die immediately when you hit them, and in JK2 that translates to health points. They will try to hit you back, and a swing with good coverage will make sure that afterblows from certain angles will hit your blade and not your body. You can read more about coverage here .