A toilet plunger works best when its flange seals the drain opening and there is enough water to transmit pressure. The goal is not brute force; it is controlled push-and-pull pressure without causing an overflow.
Do not flush again if the bowl is high
If the water level is rising, close the supply valve or wait for it to fall before starting. Put towels around the base for splashes and make sure you can work without adding more water to the bowl.
Create a complete seal
Use a flange-style toilet plunger. Tip it as you lower it into the bowl so the cup fills with water, center the flange over the outlet, and make the first push slowly to avoid forcing trapped air outward.
Use controlled push-and-pull strokes
Keep the seal and make several firm strokes without lifting the cup off the drain. The pull stroke matters as much as the push because suction can move paper or soft waste lodged in the toilet trap.
Test with a small amount of water before flushing
Once the bowl drains quickly, add a small amount of water to confirm the passage is clear. If it remains slow or you suspect a solid object, a toilet auger or plumber is more appropriate than repeated plunging.