'x' is the rarest letter in English after 'q' and 'z', and it almost never starts a word. Most words use 'x' in the middle or at the end, like 'box' and 'taxi'. The shape is simple, two slants that cross. The mistake to watch for is making it a plus sign, which is a math symbol, not a letter. Stress that 'x' is always tilted, like a star drawn with two strokes.

Two lines crossing. The simplest letter to draw, the rarest to use. Sometimes the smallest tools come out only when needed. Save 'x' for when the moment calls for it.