The volley shown here is hit with an Eastern forehand grip. If you use this grip for forehand volleys, you should switch to a modified Eastern backhand or full Eastern backhand grip for backhand volleys. Using the Eastern grips is much easier physically, because they give the racquet the best support, but it's more difficult mentally because you have to remember to switch.
The alternative is a Continental grip, which you can use for both sides. The Continental grip feels reasonably solid on the backhand side. It can be quite uncomfortable on the forehand, but the majority of players who stick with it eventually get used to it. Others (often unwittingly) use a grip between Continental and forehand, which feels better on the forehand side, but supports the racquet too weakly on the backhand side to be a good long-term solution.
For getting started with volleys, the Eastern grips are much easier, and a sizeable minority of players keep using them quite effectively into the advanced levels of play. Once you master the basics of volleying, if you can get comfortable with the true Continental grip, it's your best choice in the long run, but if your arm keeps complaining about the way it feels, pay attention. The Continental grip just isn't right for some players.
This photo shows the standard net ready position, with your left hand lightly holding the throat of the racquet.
