Hi, I turned thirteen last march so maybe I can help. Try to keep it simple. Keep most things natural. Make sure you have a lot of room and be able to have loud music. Keep whenever you have the party late at night, it helps the feel. Make sure everything is dark and has a lot of cool lighting. Whatever you do dont make it a...what's the word...type party (like luah or costume) that makes it really gay. Make sure if you're inviting people from different groups that they have friends who are coming or they might get into an awkward situation. Avoid having a cake, go with cupcakes it makes things more fun and less casual! Dont organize things, you'll have more fun just chillin and makin it up as you go along! GOOD LUCK!!!