Learn to Crochet - Blocking Crochet
Many yarns benefit from light blocking; some yarns demand it. If you've crocheted a delicate lace doily in fine cotton, you'll need to block it heavily to straighten the sides and align the stitches in order to see the beautiful lace pattern.
Small pieces can be blocked on the surface of an ironing board. Large pieces can be pinned and blocked on top of a mattress covered with clean towels. Blocking boards can also be purchased, and they are often printed with a 1" grid, which makes shaping the pieces to their measurements a snap!
Cotton: Lay the crocheted pieces wrong side up on a flat padded surface (such as the top of an ironing board or a mattress protected with a layer of clean towels), gently stretching and shaping to the measurements specified. Pin in place with rustproof pins. Dampen the piece. If starching is required (for a crocheted doily, for instance) dab the starch onto the piece using a clean cloth or a soft, clean paintbrush. Then press using a hot iron. Do not allow the full weight of the iron to rest on the work, especially if the piece contains highly textured stitches such as bobbles and popcorns. Remove the pins and, if necessary, make small adjustments to the edges of the piece to ensure that they are straight. Repin and let pieces dry thoroughly before moving them.
Acrylic yarn: Blocking items made with acrylic yarn is not usually necessary. If you feel blocking will help make the garment look better, block as for cotton items, but do not press, just let the pieces dry thoroughly before removing any pins.