The overall idea, is to make the other person, feel good about themselves, and to want to talk to you. Its not just about being entertaining and making them laugh, although if you have a similar sense of humour then the rest is easy.
When you walk into the party room, walk proudly and confidently. Possibly even pause, to survey the room, and to let people notice you.
Decide what you most want to know about a person, before approaching them. Not a list of questions but a few ideas.
When approaching someone for the first time, above all else, smile. That lowers barriers and shows an intention to be friendly.
The first thing you say should be relevant to the occasion or the surroundings, and not be too personally intrusive etc The ice breaking games, give you a perfectly plausable excuse. At our events, it does not really matter that much as most people are open to being approached, so you dont have to overcome the barriers you would get in a regular bar or club. See later for good and bad opening lines.
Take an interest in the other person. People mostly like to talk about themselves, so listen to what they have to say. However, its not an interview, so be careful. It is important to develop the other persons answers wherever possible.
Try not to offer information about yourself unless asked. You can prompt questions by offering hints, and asking the other person the same question. They will normally reciprocate.
Establish areas of common interest. If necessary, save one for later, in case you get into difficulties.
When you encounter an area of commonality, where possible let the other person finish what they have to say. For example, If they met George Clooney that day, let them be the centre of attention for a few minutes before telling them that George Clooney is in fact your uncle.
Be complimentary about the other person, and mean it, but be realistic, say you like their hair, but don't say they have the most amazing hair you have ever seen, unless its true!
If you are a guy, be chivalrous and buy a lady a drink