Robbed again!
So you've rolled 7 yet again, you need to figure out what to do with the robber. If the robber is on one of your cities, great! You're glad to finally get him off.
But what do you when you're in the lead or there's no obvious leader?
Early on in the game
Consider putting it on the desert, it might be a wise choice at the start of the game, it's pays to be deceptively nice at the start of the game, and ensures that no one holds a grudge against you for that time, especially if you blocked him and his number was rolled 8 times in a row.
Later in the game
But if the scenario changes, it's later in the game and you're the leader or there's still no obvious leader. You roll the dice and lucky 7 turns up. Do you place the robber on a 6 or 8 with a couple of opponents on them? Or do you block the largest source of brick which has been extremely hard to come by so far.I personally optto nail more than one player at a time. Sometime's it's just the logical choice, that way no one person feels singled out as a target. You could also target the resources which your opponent needs, perhaps someone is vying with you for the longest road. And their only brick resource is on a tile with a low occurance (2-4 or 10-12), it could still be good to block that opponent.
What to do when someone robs you?
The best thing to do is to play a knight or roll a 7, however both are pretty unlikely so just let it go. Focus on the main goal and don't get too caught up with the robbers. Don't let it distract you. Don't invest in development cards just to get the robber off you, unless that site is the pivotal to your victory. It will move eventually, after being satiated off the fat of your land. Your time for revenge (in-game) will come.