Fill a basin or clean sink with tepid or cool water. Add a mild soap or baby shampoo. A generous tablespoon of soap or shampoo is enough for an average sweater. Gently stir the soap or shampoo into the water with your fingertips and then add the garment, pressing gently to submerge it. Gently press the garment up and down to "swish" the water through the garment. Let the water drain from the sink or pour it out of the basin.
Refill the basin or sink with cool water and gently press the fresh water through the garment, but be careful not to twist or wring the garment. Repeat this step once more to make sure you have rinsed out all the soap or shampoo. The water should be clear.
Lay a towel out on a flat surface. Lift the garment out the basin or sink. Support its weight with both hands as you transfer it to the towel. Spread the garment out so that it's more or less flat. Roll the sweater up in the towel and press on the roll so the towel blots up the excess water from the garment. You may need to repeat this procedure with a fresh, dry towel one or two more times for heavy garments.
Lay the garment out flat on a clean, dry towel or a sweater drying rack. Use your hands to gently press the garment into its original shape. Pay special attention to seams, necklines, hems and closures like buttons or zippers. Pat the piece into shape instead of stretching or pulling the garment. Let the garment dry completely away from sunlight or radiators.
After the garment is completely dry, fold it to store flat on a shelf or in a drawer. If you are folding a sweater, try to avoid folding it so that you get a crease down the center front. Do not hang garments. Hangers can cause garments to stretch out of shape and may produce unsightly bumps.