borders, mandalas and geometric motifs
Motifs are the tradition of cross-stitch: sampler borders, repeating squares, mandalas. No photo to follow, only stitches answering each other.
The pattern maker has two mirrors, left-right and top-bottom: draw a quarter of a mandala and the other three copy themselves. A border is built from one repeated unit, and that unit is the part to get right.
A good motif often fits in two or three threads. The red and white of old samplers, the blue and ecru of Nordic embroidery: repetition does the rest.
DMC references that come up often on this subject, each with its own page.