Use Car Defroster and Patience

Using the vehicle's built-in heating system is the standard way to melt ice, although it takes longer.

Start the car's engine.
Turn the climate control system to the 'Defrost' setting (directing air to the windshield).
Set the temperature control to maximum heat.
Set the fan speed to high.
Ensure the air intake is set to 'Fresh Air' (not recirculation).
Allow the engine to warm up and the warm air to gradually melt the ice on the windshield from the inside out. This can take several minutes.
Use an ice scraper to help remove the loosened ice once it starts melting.
Do NOT pour hot water on a frozen windshield, as the rapid temperature change can crack the glass.

N/A - The standard, safe method using the car's own systems, requiring no extra supplies but taking more time.

Other solutions for How can I de-ice a frozen car windshield or lock quickly?