At the core or base of Jeet Kune Do is the By-jong stance, if you are in the proper stance you are free to move in any direction quickly.  It is what makes performing the footwork possible.
    90% of all hitting is done with your lead hand and foot, so to take advantage of this, in Jeet Kune Do we fight with our power side forward.  It just make sense that if I am going to hit you with my lead hand most of the time, it should be with my most powerful and coordinated hand.
    To get in to the By-jong stand relaxed with your feet shoulders width apart.  If you're right handed you would tke a step back with your left leg, and keep your weight balanced evenly between both of your legs.  Turn your front foot in to protect your groin, and keep the heel on your rear foot raised.  The raised rear heel helps us in two ways; first, it acts as a shock if you have to roll back to avoid a strike to the head, second, with the rear foot raised you can push off of it to shuffle forward for a quick strike.  Turn your hips slightly in and tuck your chin down.
    Your arms, although never fixed in any set position, are kept in two general areas.  The rear arm is either keep at a centerline or in a position that has become known, as "answering the phone" since that is what it best resembles.  Both have their advantages and disadvantages.  These should be explored by you so you can find what is "your truth".  Your lead arm is kept extended, and always moving, probing your opponents defenses and waiting for the opening.  We keep our lead arm extended so that it has a shorter way to travel to hit your opponent.  If your lead arm is held to close to your body, and your opponent has his arm extended, then there is no way that you will be able to 'intercept' his strike.  Intercepting is the cornerstone of Jeet Kune Do.
    The By-jong held in such high regard that it was mandatory that all techniques that were even being considered for inclusion in Jeet Kune Do had to be able to flow from it.  When you're in the By-jong stay relaxed and very light in your feet.  Don't make jerky motions; keep all of your movements smooth and small.
    In Jeet Kune Do you train the way we fight.  This means that no matter what technique we are training, you train from the By-jong.  If you are practicing your jab - hook combination on focus gloves with a training partner, or your round kick into a heavy bag by yourself, it is important that you train in your By-jong.  All footwork should always be done while in the By-jong.  It would make no sense to practice your footwork in one stance and fight in another...
    The on-guard position is that position most favorable to the mechanical execution of all the total techniques and skills.  It allows complete relaxation yet, at the same time, gives a muscle tonus most favorable to quick reaction time.  Proper posture is a matter of effective interior organization of the body which can be achieved only by long and well-disciplined practice.  The semi-crouch stance is the perfect stance for fighting because you are braced but are, at all times, in a comfortably balanced position from which you can attack, counter, or defend without preliminary movement.  This stance may be referred to as the "Small phasic bent-knee stance."