The basic breath pattern
In each four-hole block, blow gives the chord-like notes C, E, G, C. Draw fills the scale with D, F, A, B.
Why F and B are draw notes
F and B are often where beginners hesitate. On a C chromatic harmonica, both are draw notes in the middle octave.
Use breath direction as a rhythm cue
When a scale run feels uneven, speak the breath pattern before playing it. Blow, draw, blow, draw is easier to remember than note names alone.