If you think Minicon is big, you haven't seen anything. Well, you can play too. The first trick is picking a year. Eligibility is limited on one region per year, and they cycle through from East to West to Central. The current cycle is shown in the second sidebar.
International bids are eligible anytime, without upsetting the cycle.
If the Worldcon is overseas then we hold something called the NASFiC, or North American Science Fiction Convention. NASFiC is held in the region that otherwise would have hosted the Worldcon, had it been on this continent. For instance, the 1995 Worldcon will be in Glasgow, Scotland, and since this is an Eastern year, the NASFiC will be in Atlanta that same year. Worldcons and NASFiCs are traditionally held over Labor Day weekend, although overseas cons usually run earlier or later, so they don't conflict. Each Worldcon selects the site for the Worldcon to be held three years later.