As today's earlier post noted, steampunk has strong roots in the Victorian era, and much of the look and feel of steampunk is associated with that era of explorers, teh developments in steam and mechanical technology, and of course, the fashion of the day. Goggles and helmets are classic steampunk pieces, and corsets with skirts or bloomers are de rigeur for women, just to give you a flavour. Brasss accents abound. To sum it up, I quite like Jess Nevins's dry quip that, "Steampunk is what happens when goths discover brown."
It's a fun look to play with and make your own, and there are loads of steampunkers at pretty much any convention where you might expect to find some cosplay going on. To give you a little flavour, here's a great group shot I found on flickr:
(by Senna Chen & Sydney Mills, from FanimeCon 2009, via flickr)
There are tons more images to be found - try this steampunk fashion flickr pool, for starters.
If you decide to try this out for yourself, you won't be alone in creating things wth a steampunk look - a quick search on etsy turns up some 125,000 items, though some would be rejected by those in the scene as merely decorated with gears and an obvious bandwagon grab, but still, it can give you some great ideas and a feel for the aesthetic. If you're really interested in trying to make some things of your own, it's not a bad place to find supplies, either.