To dream that you are playing truth or dare indicates that you need to hold true to your words and do what you say you are going to do.
To dream that you have to tell the truth, then it means that you need to come clean about something that has been nagging on your mind. You need to release some guilt or clear your conscious.
To dream that you dare someone to do something suggests that you are being too dominating. If someone dared you to do something, then it indicates that you will find yourself in some embarrassing or compromising position.