A sack is when you tackle the quarterback behind the line of scrimmage (where the ball starts). What I suggest is having four defensive players on the line (Use the 4-3 in the playbook for this. This means 4 defensive linemen and 3 linebackers).
Now, you must run some type of blitz play. Take control of a player that isn't on the defensive line and wait near a defensive lineman (a person on the line between the offense and defense). As soon as the ball is in play, your defensive lineman should cover some players. Use your controlled player to weave through and tackle the quarterback.
To make it easier, shift your defensive line to the side where you're controlling the player. By shifting it, you'll have one side covered more giving your controlled player an easier time to make the sack.
A 3-4 defense (3 defensive linemen and 4 linebackers) will also work but maybe a little more advanced to achieve sacks. It is a good idea to mix up your plays though.