How do you wash a sweater that's a thing of beauty--and not wreck it? You chose a style that does you favors, in a color that makes you glow, knitted it with care so the stitches are beautiful, blocked and seamed it like a pro, your size and fit are spot on, and you love wearing it.
Does it fit your lifestyle? What happens when you wash it? What kind of use and care does your sweater want so it doesn't shrink, stretch, pill or die? Sweater use and care versus your lifestyle.
If you hike through brambles, drive a school bus, and wrestle with kids and pets so much there's little time for washing delicates and laying them out to air dry, your precious sweater may a) never get washed at all, or b) get tossed into the washer and/or dryer by mistake.
If not by you, then by a person who helps out in a pinch.
Speaking of pets, watch out for teeth or claws near your sweater.
They can catch and pull out a long snag in a heartbeat.
Ask me how I know.
What sweater fiber will survive the washer and dryer?

• Acrylic, better if you don't bake it to death.
  
• Superwash wool.
  
• Cotton, as long as you're aware it can stretch and sag while soggy, you don't bake it all the way dry either, and remember that some colors may bleed onto others.
  

Speaking of which, throw something red into the wash with your sweater if you just LOVE pink overtones and splotches.
You've been warned.
What fibers won't tolerate your machines?

• Wool, because it fulls or felts.
  This is where your beautiful sweater becomes doll-size.
  
• Bamboo, because it swells when wet and/or loses cohesiveness.
  

Don't hang it up! Sweaters prefer to lie quietly in a drawer when not being worn.
Otherwise they'll grow wicked pointy shoulders on your hanger and stay that way when you wear them.
Not a good look.
So to recap, here's how to wreck your gorgeous finished sweater.
Toss it in a basin or the washer with hot water and harsh soap, with an item that'll bleed on it, and agitate it like it got filthy in the Labreya tar pits.
Yank it out while wet so you stretch it out of shape.
Bake in a million degree dryer for a week.
Ta-da! Your sweater is now unrecognizable, unwearable and can't ever be brought back to vibrant life.
Yes, I could cry along with you.
Here's hoping you or a loved one will NEVER wash a sweater wrong.