What is the best technique for applying spackle to drywall to achieve a smooth and seamless finish?

The best technique for applying spackle to drywall to achieve a smooth and seamless finish is to apply multiple thin layers, allowing each layer to dry completely before sanding and applying the next layer. Sanding between layers helps to create a smooth surface, and feathering the edges of the spackle helps to blend it seamlessly with the surrounding drywall.