There are hundreds (literally) of theme ideas out there and here're a few to start with. You may try a 'Caribbean Night' party. You are not, of course, expected to bring all your guests to a beach but you can all, at least, pretend. A good outdoor setting would be okay, just add up some fake palm trees to suit the mood. Have your guests dress in brightly-colored clothes and let them listen to a lot of Bob Marley songs all through the party.
For the kids-at-heart, you may try a 'Children's Party' for the adults. Have your venue decorated with lots of colorful helium balloons and throw lots of party poppers around the place. As for your guests, have them come dressed in their a high-school uniform (if it still fits!), or if you prefer them in a superhero costume then ask them to do so. Give life to your party by throwing in a lot of kiddie games that will surely make you all laugh like kids.
A 'Masked Ball' is also a great idea. Have a glamorous black-tie party with everyone hiding behind a mask. Keep the venue simple and elegant, do not overdo the decorations. Make your guests experience one dazzling event after another with enchanting music and great drinks. And yes, you may all dance the night away feeling like princes and princesses.
For a great theme party, why not let Drinkdings, --- Your mobile bars solution TM, handle it for you? Drinkdings organizes theme parties, all complete with programming, games and prizes, music and performances. All that's left for you to do is enjoy the party with your guests!
If you have no bartender with you then serve the drinks yourself. You have to be sure that everyone has a drink in their hands. And last but definitely not the least, enjoy your own party. If your guests seesaw that you yourself the host is enjoying the event, they are most likely to enjoy it, too.