This is another simple stance, particularly if you have mastered the walking stance. Imagine that you are standing in a rectangle which is as wide and as your shoulders but much deeper than your shoulders. How deep depends on your flexibility, if you are relatively new to martial arts then it is best not to make it too much deeper. A rough rule of thumb is to assume the walking stance and then move your forward foot forward by a foot length. When performing patterns it is best to make it clear that there is a difference between your walking stance and forward stance; however be careful not to overstretch and loose balance or hurt your ligaments.
Place your left foot forward to the top left corner of your rectangle.
Place your right foot behind to the rear right corner of your rectangle.
Keep your feet pointing forward so the effect is like being on tramlines, and bend your knees a noticeable amount (your rear leg will be stretched out and approaching being straight). Your hips should be at around 45 degrees, while your shoulders should be facing the front. Your weight should be evenly distributed between your feet.
There are many possible positions for your hands in the stance, but we'll start with a basic lower block. Hold your hands out as far as they go in front at shoulder height palm downs. Now rotate your hands so that your palms face each other and bend your elbows bring your hand towards your body. Position your left hand further out so that the line of your hands is similar to the line of your hips.
Moving forward, or back, consists of moving the rear foot to the front in a straight line (so like the feet are moving on tramlines).
The side which your tummy is facing is call the open side, and the side that your back is facing is called the closed side. In sparring the idea is to kick to the open side (where all the soft bit are), rather than the closed side (the more protected back).
The stance is easy to move into, particularly if you start in a walking stance. The stance give a fair degree of stability as the rear leg is a brace against any forward pressure; as the stance is low it is stable from front pressure. It is a good attacking position for responding to a head punch. For example: You are in a walking stance and the opponent punches to your head (straight punch or roundhouse). You move forward with a rising block, to deflect the punch, then follow this with a reverse punch to the body. This is quite effective at stopping an opponent charging in.