If I have my 12th birthday party what kind of games should I do?

It depends on where you are going to have your birthday party. If you want to have it at home, then organize games for the gender of people coming to your party. One thing everyone loves is popcorn and a movie. Also, you can use normal games, such as Pass the Parcel (if you don't know what that is, google it) and involve prizes (candy tends to work well), so that it will be more fun. Competitive games are always enjoyable, especially if there is a prize. If it is an all girls party, you could try nail-painting as well. Also, 12 year old kids enjoy music, so maybe involve some dancing or even a dancing contest.