Feet 45 degrees drill
The golf instructor explains what normally causes a slice, which is people coming over the top or rather their swing is coming from outside to in, which is the opposite of what should happen.
To setup for the drill, have your feet aiming 45 degree left from the target, then align your shoulders and club face at the target, like you would do on a normal swing
Once the setup is correct, during the swing you want to focus on swinging the club out too 45 degree right of the target line.
To make this drill effective place clubs at each of the lines to act as guide lines
Other topics that might interest you