If I could only state one goal in a party planning guide, it would be this:  Strive for the party that everyone will enjoy. That involves a little more than simply doing what might be fun for you and inviting everyone you know - it means thinking things through (and perhaps adjusting accordingly).

A cocktail party may be pleasurably memorable for the specific people lucky enough to find congenial others to talk to... but it’s highly unlikely to be pleasurably memorable for the whole group. A focal point or theme party, though - if the focus/theme is chosen to suit the participants - is very liable to achieve this goal...

...As long as at least one person (usually the host) is committed to drawing people into the vortex. In a cocktail party situation, one person just isn’t enough - the milling about and seeking of targets that’s de rigueur precludes much comfort for the person who doesn’t already know everyone intimately. In a group-focused setting predisposed to cohesion, it takes much less to tip the balance... Still, it wouldn’t hurt to appoint a few people to ensuring that everyone is being included in the enjoyment. (By this I absolutely do not mean patronizingly pushing people to "join in!" - I mean sensitively appraising the situation and creatively seeking solutions for wallflower tendencies!)

Hmm, old-fashioned ice cream-making parties are good mixers - and who said winter means no ice cream?... silly idea. (Besides, you might live in the southern hemisphere and be sweltering.) Teams can make their own flavors... and everyone takes turns mixing, literally as well as figuratively. How about a cone-decorating contest? (By the way, ice cream cones can be filled with things other than ice cream... fruit salad, for instance - mmm.)