Drill 108 from FineSoccer.com

Here is an excellent way to work on possession, penetration and runs inside the box.  Start with a 4 v 4 (plus keepers) in a 60 x 40 area with two full sized goals (you can use more players on the inside by adding space).  There will be 4 players on the end lines (2 on each end line).  See diagram below to see the set up.

The basic rules of this game are that it's a normal game of soccer with the exception being that a team can use the players on their offensive end line.  The players on the end line are limited to one touch.  The idea of this game is for the field players to look to maintain possession until they have set up a situation where they can either go to goal or find a player on the end line to initiate the runs in the box.  To see an example of the type of scoring opportunities that can be created, see the diagram below

There are many other options that can be added into this activity (including putting players on the side lines as well who can provide support for either team).