Staying calm yourself is one of the most important things you can do. The more agitated you become, the more likely the person with dementia will also become agitated.
Try using a distractor that gives them pleasure—a TV show that calms them down, a food they enjoy, or a walk looking at a garden.
Sometimes a diversion will reduce the agitation. Sometimes there is an object that will help calm someone down. For example, many women are less agitated when holding their purse.
Photo albums of happy times may also be useful in helping to get someone to calm down. And many people are finding music a wonderful way to help soothe someone with dementia.
You may want to fill an Ipod with music that would be soothing and enjoyable to the person you are caring for. If you notice they are starting to get agitated you can gently offer them the music.
You might want to see if there is a pattern to what causes the agitation. Sometimes it is too much stimulation in the environment. If that is the case, remove the person from that environment to a quieter and calmer one.