This can be a very difficult shot for almost everyone. Where most people get in trouble is they try and make their normal swing. Because of this the club comes in at to shallow of an angle and they get to much grass between the clubface and the ball.
You have to check the lie and see how much grass is behind the ball. The goal is to try and get as much club on the ball as possible. You will need to come down at a much steeper angle, the deeper the grass, the steeper the angle. To insure a steeper angle you should play it back in your stance a little bit and it will probably feel more like a chopping motion, depending on how thick the grass is.
Strength is definitely a major asset for this shot. Not only for getting through the grass but also to stop the clubface from twisting to much.
Depending on the length of the grass and the density of it you may only be able to advance the ball with a short iron. If you remember back in the day when the USGA would grow the rough incredibly high, even the Touring Pro’s would just pitch it back out into the fairway.