The grip: Semi Western
The ideal grip for this stroke is a semi-western grip which is the most versatile for different types of shots on different surfaces. Using either a western or continental grip can hinder your ability to generate spin on the ball. Western grips will allow for heavy topspin on high balls but it can be more difficult to create pace and spin on a normal delivery.

The stroke:
The stroke itself is the regular low to high swing finishing above your shoulder at the end of your swing. When making contact with the ball, your racket should be slightly closed so that you can “brush up the back of the ball.” This is achieved by the correct swing, if you do not finish above your opposite shoulder when you finish your stroke then one of two things are likely to happen:

1)      The shot is not powerful enough and will spin into the net (or earlier!)

2)      The shot will contain very little spin as there was little “brushing”

See the below images to see how an example of the top spin forehand.

The knack:
The trick to the topspin forehand is to generate lots of racket head speed using your upper body. The racket face must remain closed to create the spin, so you are relying on generating the racket head speed using your upper body to carry it deep over the net. Try concentrating on a smooth, fluid swing to gain momentum and generate the pace required. A fast unconnected action will make it much harder to get the ball over the net.
A final trick is to snap your wrist (not literally!) to generate that brushing motion over the top of the ball.

Now look at the video above to see how the pro's do it and get on court and try it for yourself!