Sometimes I find that the plunging won't work. It is because beneath the rim of the toilet there are holes where water comes out when you flush. When plunging, these holes interfere because they allow air to escape, so you are pushing air out of the holes rather than attacking the clog.
What I do is take the cover off of the tank and find the flapper valve, then I flush the toilet and wait untill it is about to overflow, at this point the water has risen above the rim bottom and covered the air holes, then I close the flapper valve with my hand so the toilet won't overflow and start plunging. It helps to have the plunger in posistion before starting. Since the water is covering all of the holes where air could escape from, the plunging works better. Just make sure you are ready with the flapper valve because you don't want the toilet to overflow. It's handy to know where it is anyway because if the toilet is ever about to overflow, you can close the flapper valve to stop it from happening.