Preparation

The X block is more of a transition between movement.
The X is in front of your face, you're looking through the top and you've crossed one forearm over the other and you've got tight fists
Feet are separated a little bit more than shoulder distance apart
Toes are pointed straight ahead, knees are bent, back is straight and you are going to start shifting and turning
There are two Xs.
There is the right X where the right arm is on the outside (for right arm blocks) and then the left X where the left arm is on the outside (for left arm blocks)
You can break a grip using X transitions

Teaching

Spread your feet slightly wider than shoulder distance apart, and keep your toes straight ahead, knees bent, back straight, and with an X block.
Blocks are strikes
When in X block your weight should be centered, while blocking it should be approximately 60/40 or 30/70
Return to your X between blocks
Overhead block: turn and lean to drive your forearm up knocking the target away which is the opponent's punch.
Outside block: Turn and lean and drive your arm outside with the elbow down with the shoulder turned towards the opponent
Low block: You're going to turn and lean. A strike is coming in at the belly or groin. Drive down leading with the elbow and block out
Work on technique first, then power, then speed.