A great party has a theme. Build with entertainment (such as music or games) and a great theme menu. Decorate with the theme in mind to make a really fun party! Dont forget to give some type of goodie bag.
If you want to throw a really great party, make sure that you have a lot of food and drinks, as well as may activities to do. Fun things are board games and video games. Also, music is a necessity.
The best way to throw really fun parties in my opinion is to start with fun people on the invitation list. After that plan some activities, like charades or pictionary. Can't go wrong there.
The best parties I've been to have a lot of people, a lot of alcohol, games, good music, and food. If you can take all of these things and put them in one place then you will have an awesome party.