Turn off the water supply to the toilet
Remove the tank lid and check the water level
Use a plunger with a good seal over the drain opening
Plunge firmly several times
Flush to see if the clog clears
Use a toilet auger if plunging does not work
Insert the auger into the drain and crank it to break up the clog
Remove the auger and flush again
Repeat plunging or augering if needed
Avoid using chemical drain cleaners
Clean up any spilled water
Call a plumber if the toilet still will not drain