Your turn is almost over. What's going to happen next turn -- is your opponent going to be able to place his plan into action, or will he be forced to respond to you? So long as he's responding, you're probably winning.

One good way to keep your opponent responding to you is to give him a serious problem to respond to. If your enemy puts his plan into effect without responding to whatever serious problem you created, you'll have gained an advantage; if your enemy solves the new problem you created, you prevented them from putting their plan into action.

Let's take an example. Suppose you've knocked a hole in a border and have taken several border states. Sure, you don't have the armies to hold the whole continent, but why not push forward and take it? Then your enemy has to re-take at least a part of the continent next turn, or accept you gaining that production. If your enemy was counting on his new production to put his plan into effect on the next turn, he'll either have to execute his plan without the added armies, deploying them instead to re-take a portion of your new continent, or have to accept you holding another continent while executing the plan as originally foreseen. Either way, not a great option.

And either way, you've got the initiative, not your enemy.