In a situation where outbreaks chain into other cities, how can I manage cube placement so that I know which cities I've resolved? If I just place the cubes into the city, it's easy to lose track of which cities still need cubes.
I normally place the 4th cube on top of a triangle of the three existing cubes in the infected city. Then, place a cube in all it's neighbours and move the outbreak meter up 1. Move the 4th cube off the stack of three and place it on the board (making a square) to show you've resolved that outbreak. Repeat for any other cities which just received a 4th cube (which is on top of the pile of 3). Once you have finished, remove all the 4th cubes which are on the board.
The first outbreak is easy to track, because it is the green card that you are currently resolving. It is very rare for outbreaks to chain more than 2 deep, but if you find yourself in that situation, you could use a cube of a color that the city is not adjacent to and place it in the city to temporarily mark that you have already resolved outbreaks there this turn. Just remember to pick those "wrong color" cubes up afterwards, or you will be shorting your supply.