It's smart to bone up on both. Read the yard sale ads, and spend a morning or two visiting neighborhood sales. Note price ranges on clothing, kitchenware and books. There's no sense labeling two boxes of kitchen utensils at 50 cents if a quarter is the going rate. Check with your municipality and homeowners' association.
Some jurisdictions require a permit, or limit the number and timing of yard sales.
Set a date. Have a strategy for sale's end. Many charities will pick up all unsold items. Call and schedule a 3 p.m. pickup for sale day, or be prepared to box the leftovers for delivery to a thrift store donation site. You've sorted your stuff and scoped out the field.