It really depends on the species around you. I know of 3 large flights every year that I run into simply because I practically live outside in summer, and those species fly by the thousands in my location. That being said, I can go over a month without seeing any queens.
For species with smaller flights, it is more of a case of luck in finding them. You can also watch the Ant flight list for when people post flights in your area.
For people who don't go outside very much, you options are a bit more limited. Do you have a pool? Check it several times a day. Do you have an outside light? Replace the bulb with a blacklight bulb and drape a sheet under it, check it every couple hours at night while the light is on.