I like to follow real-life ATC procedures as much as possible when playing ATC-SIM. I'm reasonably familiar with O'Hare, so here is a summary of how that airport operates (please correct any errors you see). I'd be very interested in seeing summaries of other airports.
I realize that there are limitations to applying these procedures to ATC-SIM, but I hope this can still be helpful. These procedures apply to ORD in its current state, before the opening of 10R/28L but after the permanent closure of 14L/32R, so a new summary will be needed soon!
Airspace overview: ORD airspace is organized so that (most) arrivals enter at the corners of the map and departures leave at the sides. The preferred traffic patterns are West Flow (most common), where planes take off and land westbound (mostly), and East Flow, where takeoffs and landings happen eastward. There are other flow arrangements that are used when necessary, but these are much more tricky to coordinate and throughput is significantly reduced. (I have listed these alternative flows at the bottom of this message.)
Note that "heavies" most often arrive on 10C/28C and depart from 10L/28R, but exceptions to this are common.
Arrival summary: Arrivals are typically routed to two east-west corridors. One runs through fixes KURKK and VULCN on the north side of the airport, and is used for arrivals to 9L/27R. The other corridor runs through JORJO and MONKZ on the south side with traffic for 9R/27L and 10C/28C. Once in these corridors, controllers will turn aircraft into the approaches for the runways as spacing permits. Because heavies usually land on the south side of the airport, those entering north of the airfield often cross over the airport to join the southern corridor at JORJO or MONKZ.
Departure summary: Departures are usually routed directly to their exit fixes very soon after takeoff. (O'Hare does not have any published SIDs.) However, if the departure fix is in a direction opposite from takeoff, aircraft are often routed to two informal east-west corridors that are farther away from the airport than the arrival corridors. For example, a takeoff from 9R with a destination of MYKIE will often be routed northward past the KURKK-VULCN arrival corridor before turning west.
West Flow summary: Arrival runways are 27R, 27L, and 28C. Departures come off of 28R and 22L. You might think that 32L would also be a good choice for departures in this configuration, but the conflict with potential missed approaches on 27R and 27L complicates the timing of departures so it doesn't actually improve throughput in real life.
Arrivals from the northwest converge on the northern arrival corridor at KURKK for landing on 27R. Arrivals from the southwest converge on JORJO for landing on 28C. Arrivals from the northeast (usually for 27R) and southeast (usually for 27L) are routed more vertically (on the screen) to their runway approaches.
East Flow summary: Arrival runways are 9L, 9R, and 10C, and departures use 9R and 10L. You'll notice that 9R is shared between arrivals and departures. 4L is not often used in this configuration because it conflicts with both 9L and 9R. There are also occasions when 22L may be used for departures.
Arrivals from the northeast converge on VULCN for landing on 9L and those from the southeast converge on MONKZ for 10C. Arrivals from the northwest (to 9L) and southwest (to 9R) are routed more vertically to their approaches.
West flow with northward departures: Arrivals on 28C & 27L, departures on 32L & 28R. This is for low visibility conditions which coincide with 22L not being available for departures.
"14's": Arrivals on 14R, departures on 10L, 9R, 22L, or 4L. This would allow landings with strong winds from the south or southeast. The closure of 14L makes this flow less useful.
"22's": Arrivals on 22R & 22L, departures on 28R, 27L, 32L, or 22L, for strong southwest winds.
"4's": Arrivals on 4R & 4L, departures on 4R, 4L, 32L, 9R, or 10L. This is only used when strong winds from the north make East Flow or West Flow impossible.
More information Sources for arrival and departure procedures: (airnav.com is often more up-to-date) http://www.airnav.com/airport/KORD http://flightaware.com/resources/airport/KORD/procedures
FAA document that includes overviews of current and future traffic flows: http://www.faa.gov/airports/airport_development/omp/eis_re_eval/
Pilot Awareness page describing upcoming changes to the airport: http://www.flychicago.com/OHare/EN/AboutUs/PilotAwareness/Pages/Pilot-Awareness.aspx