If you plan to wash your sweater, you should wash it in the manner that you would wash your sweater.
If you are using a wool product that does not say "Superwash" on it or is not blended with acrylic, some other synthetic fiber, or cotton, you should handwash your garment. Handwashing alos prolongs the life of any fiber.
Fill your bathtub or your washing machine with luke warm water, dissolve a VERY GENTLE soap in the water. Some people like to use Euclan or some other wool-friendly soap. Some people just use a mild shampoo. Swish the soap around to let it fully dissolve. Place your garment in the water and allow it to soak.
DO NOT AGITATE
DO NOT POUR WATER ON TOP
These things will cause the wooly fibers to open up, rub together, and start to lock together, creating a fabric knows as felt. This is the process which causes woolens to SHRINK. Sometimes this is okay, as in making a purse. Mostly, it is not desired.
Drain your tub or machine. Fill your tub or machine again with clean lukewarm water. You want the same temperature to prevent shocking the fiber. Drastic temp changes can also cause the fabric to felt. Allow your garment to soak again, to rinse it out.
Remove the garment and place it on a very thick towel and roll it up, squeezing water out as you go. Once this has been done, allow your garment to dry flat, pulling it into the shape you wish it to retain once it has dried. You could turn it over once one side has dried completely, but only if you can duplicate the results of your tug-and-pull game you played earlier to shape the garment as it dried.
If you already knew how to do this, I'm sorry, but I would've hated for you to have washed your first garment and had it shrunk to a size fit only for a poodle.