Have you thought of setting up your next birthday party as a 70s fancy dress dance event? There are so many things you can do to make it really swing. For example hire the movie Saturday Night Fever and have it running.
Here's a good game to play. Record some clips from Saturday night fever etc . Now have a couple watch an excerpt from it and get them to dance it out to disco music in the background. Someone's going to mess it up and cause a good deal of laughter.

Get some shiny stickers cut out of aluminum cooking foil and stick them on an plastic football. Now tie some string to the ball and hang gold and silver beads from it.Now stick it on the ceiling as your reflective dance globe. An odd spotlight on it will enhance the effect.

Next up start gathering together some disco clothing from shops and markets. There is no greater fun for guests than to rummage through the box and add to their costumes for that extra 70s effect.

Next up, take a look though some party game books or search some out online. Pick the best dance games and costume contests you can find. They will help build up the atmosphere.

Next you can set up a dance instruction spot during the evening. Line up the best dances and break them into simple steps for people to pick up.

A great way to end is the costume contest. You can do this on most spectacular wig, highest heeled men's shoes or who is wearing the loudest coloured costume.
If you string some of the above together and add some stuff of your own, your party will work really well. It only takes a little effort to make your party one that will be rembered.