The grid method breaks a reference image and your working surface into matching squares, so you can copy shapes and proportions accurately square by square instead of guessing at the whole picture at once.
It removes the guesswork of “does this look right” by turning a complex image into dozens of small, easy comparisons — the same technique professional illustrators and muralists use to scale references up or down accurately.
Pick a reference image (or a piece by the artist you’re studying) with clear, high-contrast shapes.
Lightly draw an evenly spaced grid over the reference, or over a printed/traced copy of it — start with a simple 6×8 or 8×10 grid.
Draw the same number of grid squares, scaled up or down, onto your working surface with a ruler and light pencil.
Working one square at a time, copy only what falls inside it — ignore the rest of the image so you’re comparing small shapes, not the whole picture.
Step back periodically and compare the whole drawing to the reference; look closely at square boundaries where a line doesn’t quite connect.
Once your proportions are locked in, lighten or erase the grid lines and continue rendering normally.
Try the same reference at two different grid densities (say 4×6 and 10×14). The denser grid will be more accurate but slower — notice where you personally start losing patience and accuracy.