Another excellent rule I have played with in the past is a max placement of 10 armies on any given country for one turn.
So if you have 18 armies to place, a maximum of 10 can go on one country leaving you with 8 left to place. The next turn, you can place an additional 10 armies on that same country if you want, but only 10 per turn.
This helps to control excessive hording which some people like and some don't.
It would be a good option for a rule anyway.
Thanks!