Defend Your Territories - But With Attack Squads
-Having a large army as an attack squad can dissuade potential poppers by fear of retaliation alone. In addition, your attack squad can and should be used to make kills.
In this case, the best defense is a good offense.
Place Attack Squads at Choke Points
-Fortifying inward takes away armies that can be better spent killing. What are you, the sheep, or the wolf? Find your choke points and get your armies there.
Keep An Eye on the Info Window Between Turns
-Always be seeing how many cards you have, and how many cards/armies/income others have. This should guide your strike - not the pretty color bar that simply shows a player's size.
Be Aware of How Much Cash Is Worth
-You'll likely get attacker's dice... but you need to decide before a kill if the cash (and possible double cash) will be worth the kill. In other words, will the kill put you in a stronger position than you were before... or will it make you fodder for the players who are following your turn. Can They Cash?
Don't Let The Game Get Personal
-Solid moves should be received with respect and a cool head... not returned with a suicide.