I decided to put this in hardware, not really sure why. There's not much to be said about airlocks, so this thread will probably be short.
Universal airlocks must exist to ensure you can dock to any vessel. They should be able to extend out from the surface of the ship to allow docking with poorly designed ships that have their airlock(s) in an awkward position. Universal airlocks will only have one size and shape, most likely a circle with a slightly-larger-than-person diamater. The circle makes any docking orientation possible, which is needed as there is no up or down in space.
Other airlocks can have various shapes and sizes but may not be compatible with different airlocks.
All airlocks that aren't operated by hand should include controls outside and inside the ship as well as inside the airlock. Both electronic and manual airlocks should have either a warning system and/or prevent decompression/recompression if one of the entrances is not sealed. It should be impossible (unless an enemy programs your CPU otherwise) to have both entrances open at the same time.
When building the ship, I suggest the airlock "room" only includes two doors on either end of the chamber and the air pump system. Automation/Electronic operation can be an upgrade, as well as a faster pump and maybe even some kind of sterilisation device.
Internal airlocks must also be considered. If there is a fire on the ship or a hull breach, sections of the ship will have to be isolated to prevent shipwide oxygen/atmosphere loss. For manual doors, every doorway must have two doors built in, that close in opposite directions. When approaching a doorway the door closest to you should close away from you and the one behind it close towards you. One of these doors, although manually operated, will close automatically if there is strong enough airflow (i.e decompression from a hole in the ship) in a certain direction due to its positioning.