Unblocking your toilet doesn't have to be a messy job, but if you need to remove a clog from your toilet, it’s important to stop flushing before it overflows! If one flush hasn't unblocked your toilet, then adding more water isn’t going to fix it; you’re not likely to dislodge the blockage this way, and it can cause your toilet to overflow all over the floor. You'll need a little bit of room to move above water level to keep splashing to a minimum too.
Start by putting on some rubber gloves - you may also want to put on some old clothes, just in case. Spread newspapers or old rags around the base to prevent spillage from going anywhere, and to help with clean up later. From here, there are a number of methods that basically break down into removing the clog chemically or manually. Which one you use will depend on what's blocking your toilet.
Chemical methods are good for organic blockages only. If you know the blockage is an object, move straight to the manual methods. You can use the baking soda and vinegar cure-all which is accomplished by pouring a box of baking powder into the water and then slowly adding a medium sized bottle of vinegar and letting this set for a few minutes, then adding a pot full of hot (not boiling) water and letting it sit overnight. If this doesn’t remove it, there are commercial drain cleaners which can be used, but caution needs to be exercised as if they are used improperly, it can make the clog much worse.
Manual methods include plunging, using a wire coat hanger and using a drain snake. These techniques should be employed when the clog has been caused by an object such as a child’s toy. Though somewhat messier and definitely more hands-on, sometimes this is the only way to get water flowing through your toilet again. Should any of the above fail to work, your best bet is to call a plumber.