What do I wear?

Every (kind of) synagogue has its own unwritten rules on what is acceptable and what isn't, but you can't really go wrong with the simple ones outlined here. First of all: if you are in any doubt about what goes, just wear formal and somewhat modest dress.

This is easiest on the men; a presentable suit will do nicely. It is customary to cover your head with a yarmulke or hat, and most synagogues have a little stock of kippot for the forgetfull male. But if you're going to take the trouble to look nice, it would be a shame to resort to the shul's 'emergency kippa'. These usually spend their time bunched-up in some basket or corner and can immediately be spotted by their wrinkled, slightly shabby look. It's no great hardship to buy your own 'emergency' stock to go with your nice suit or tie: there are kippot in every conceivable size and colour  to be had for a snip.

Religious women will wear modest clothes that covers knees, elbows and collarbone. You don't have to take things that far, but do leave those trousers - no matter how smart or skirt-like - and that short little skirt in the cupboard, because you're sure to feel awful if you turn out the only one decked out with one of those!
Observant or even slightly observant women will cover their head in synagogue. This is absolutely not de rigueur - but of course it is the most wonderfull opportunity to finally wear that smart  festive hat !

And as for the party: well, that's a party. If you don't go for an extensive decolleté you can't go wrong. For men, this is a more suitable place to wear a brilliant kippa such as the Buchari one featured here - but if you're lucky, you might be given a personlized kippa to commemmorate the occasion!