A tactic I learned while playing the latest BOTM. When conquering cities on a different continent, if you capture a city then gift it immediately to your colony, it will not get any free defenders. If this is during an extended conquering campaign it means you will have to leave some troops there to defend it. It is much better to wait until the next turn to gift the city to your colony because then it automatically gets 2 defenders at your current tech level. This will free up your troops for further acquisitions.

You can do it on the same turn, as long as you use the alt-f1 key.