Well Dandoon no offence but that sounds good fo a 13 year old party. Ok listen, Dandoon was right about the music, if your not ure which tunes to play then get a few friends to decide. Honestly its better if you ask questions :) next if i was you i wold try and keep your mum and dad out of the way and if they are, get some alcopops (nothing strong for the feather-weights).
And yes it would help if there are seats, chairs, sofas and a table since nobody will want to be on their feet all day/night. Truth or dare is kind of a 13 year old game you would play a few years back but if there is a girl you like, try and convince one of your mates to suggest it to everyone ;) food is a must for people who get hungry or looking for a munch.
Finally, if people are finished with dancing, get something entertaining out (im not thinking of board games) but something along the lines of contests, etc. And DONT keep playing the same songs over and over, only a really good song twice maybe 3 times if it has a good effect. Let people roam about aswell, some people will form in their own groups throughout the night and all will be doing different activities mostly. If nobody is dancing, get you and your friends in the center and get things started, if your shy about dancing then get someone who is outgoing and good at dancing to get everything started.
Anyways, have a nice birthday.