Don't mix Drill and Shock promotions on one unit - usually take Drill

[weregamer1]

You have to have multiple levels of one or the other to open up other, more valuable lines of promotions, so mixing Drill and Shock will mean you rarely see March or Blitz.

Because defending on open terrain is a -33% penalty on top of the lack of a terrain bonus, players (even the AI) will rarely want to leave a unit in the open if they can help it so more fights happen on Rough terrain.

That said, often cities have a lot of open land around them...