Music
MUSIC! Very important for any Party.
This is something to start with from the moment organizing a Party pops up in your mind. Make playlists, add as many songs you want, you can always delete songs 1 week before the Party.
Important for choosing the best musical mood: know your audience and stay true to your theme.
If you have the luxury having a DJ, tell him/her exactly what you expect an what kind of music you need. Be very clear because the mostly love to play their own favorites and that's not what you want.
Switch in your playlist between songs that fit the theme and song that are known by everyone or that brings back memories.
Always try to make people dance and do create an area where they can show their moves. Nothing more fun than hearing your guests cheering when a song starts that they love and know.