Taken from Seamless Crochet: "Worked from the bottom up, a shawl is usually decreased on either side of the center and each side edge, to create a decreasing triangular shape. To achieve this design in motifs that join as you go, we convert the square motif into triangular motifs for the decrease section (thereby reducing additional motif edges for the next row of motifs)."
This pattern is from Seamless Crochet, pg 17 - Blissful Flowers Shawl
Size US H crochet hook (or size needed to obtain gauge) is required but not included.