That plan sounds brilliant - what kind of people are coming? Are they young/old/mixed, bohemian/straight-laced/academic/political, where do you know them from?
I have always found that some kind of fire (if you can bear the worry of it getting out of control) tends to make people use the garden even in the depths of winter and provides a focal point for the shyer men. We used to have one of those bins with holes in that we burned scrap wood in at parties, or a barbeque is always popular.
My parents tend to run simple games at their parties (shit the nail, daft magic tricks, that one where you take turns to pick up a box with your mouth), but there tends to be much wider age ranges (from children up to the elderly). My parties tend to involve somebody strumming a guitar and leading a singalong with people playing along on various improvised instruments.
Cocktails are always good-will it be a bring a bottle affair? In which case, mixers and daft cheesy cocktail accessories as well as a cocktail mixing book always go down well.
Also start making ice about a week early. You can never have too much ice. Also make sure to provide some half decent non-alcoholic drinks, if you can't drink for whatever reason you quickly get sick of lemonade!
Fancy dress is a good icebreaker, as long as people don't take it too seriously. I like to give the party a purpose, look up on the internet if it is the anniversary of something and slightly theme stuff towards that. Don't go OTT though, it's just as an icebreaker for people who don't already know each other to get talking.
I tend to make a playlist on the computer and try and keep people away from it, although my mates tend to be music geeks and all are either DJs or think they are, so each try to take over the music and it becomes a pain in the bum.
What kind of size of party are we talking?