Wait for the Water to Go Down
Before plunging your toilet or doing anything else to try to resolve a clog, allow the water to go down as far as possible. The plunger will only succeed in splashing water all over you or your bathroom floor if you try to plunge while the toilet is full.
Normally, after about 10 minutes, the water level will go down to a level you can work with. Under no circumstances should you flush the toilet again, as this will likely cause it to overflow and will not resolve the clog.
Plunge Slowly and Steadily
Your plunger should fit into the mouth of the drain at the bottom of the toilet. Push the plunger into the drain and plunge slowly.
Your first few plunges will cause water to splash, and you want to minimize this effect. Plunge steadily but slowly, only occasionally plunging with more force.
It should take about 20 plunges to unclog a toilet.
For the most part, you want to avoid putting chemicals into your toilet. Chemicals may not affect the clog in the way you want; in some cases it may make the clog more resistant to dissolving instead of less.
If the chemicals fail to work, you will end up with a toilet full of polluted water. If you are facing chemical failure, pour clean water into the toilet and let it stand for 24 hours.
Put on protective goggles and gloves before plunging.
Use a Closet Augur Snake
If plunging steadily fails to resolve the clog, use a closet augur snake, which has a protective covering so that it won't damage the enamel inside the toilet bowl. If you cannot put the snake into the bowl without removing the bowl, call a plumber for assistance so that you don't damage the bowl when removing or replacing it.