I love the cross step. It is a quick way to change my orientation with respect to the opponent, and can open up targets that might not be available otherwise with almost no telegraphing. It’s not a stance you want to stay in, though, because the legs end up crossed and you can get tangled in yourself.
A front cross step, as illustrated in the first figure, involves moving the forward leg in front and “across” the back leg. For example, if I’m in a right N stance or fighting stance, I will move my right foot leftwards. This orients me now to the right side of the opponent’s body. Note that the right foot is pointing towards the opponent, not necessarily straight forward.
Similarly, a rear cross step involves moving the back leg across and behind the front leg. This stance orients me more towards the left side of the opponent. The back foot will probably also be at an angle to support a more stable stance. One mistake that students sometimes make is to accidentally shorten the stance with the cross-step, especially a rear cross step (see the third figure). This results in a stance that’s much less stable and mobile.
I’ve found that the best way to practice the basic cross step this is to have the moving foot on some kind of visual reference, so you can actually see whether your foot is going straight or whether it’s creating an unstable stance. You can draw a line with some chalk, use tape, or even practice on a tile or wood floor, using the planks or squares for reference. Sometimes improving your ability to cross-step will require work on your mobility as well as your proprioception in order to regularly move the foot straight and across for either the front cross step or the rear cross step.
When practicing the cross step, start in a middle N stance. Practice moving either the front foot or the back foot in a straight line, and then try out different ways to return to an N stance (either the same one you started in or a different one). See if you can do it without looking at your feet – can you move your foot in a straight line? You can also work this from an H stance, seeing how deep you can cross in front or behind. This really works your legs and strengthens them as well!