When you manage to get your opponents elbow to or close to centerline while in closed guard you will find yourself in truly advantageous position. Basically, anytime you can get the opponent’s elbow inside his shoulder you are in a great position to enter the high guard position or top lock.
The main attack from the top lock position is the armbar due to the nature of the trapped arm. You can attack the armbar from the back or sweep the opponent to his back to finish the armbar from there.