There are two things that are absolutely necessary before you can even think about backspin. First you need to be using a soft ball. The best ball for creating spin the Titleist Pro V1 ball. Second you need to have sharp and clean grooves. If you have these to points covered you are half way there. Place the ball in the back of your stance. You must strike the golf ball on a downward motion. Most amateur golfers try to lift the ball which will result in no spin. The club must contact the ball before the ground.

The ball then gets trapped between the club face and the ground. It is like your pinching the ball to the ground. Then, with no place to go, the ball rides up the clubface catching the sharpened grooves, hence creating spin.

Stay in the fairway. Hitting out of ruff will greatly decrease the spin on the ball. There will be a barrier of grass and debris between the ball and clubface or the ball and the ground. You will not get the trapping of the ball from the clubface and ground. So you will not get as much spin.

Note:

The best club to have controlled backspin is the wedge. All though it is possible to use a 7-iron, it is extremely difficult and should be left for the professionals. A great way to practice is: set up a small line directly in front of the ball. After completing the shot, the divot should be just in front of the line.