When a player decides to move forward during the point, most approach shots should be hit down the line and volleys should be hit crosscourt.
If the approach shot is hit deep and down the line to one side of the court, the player can move more towards the direction of the approach shot and cover the most likely reply from the opponent. Crosscourt volleys will result in angles that force the opponent to hit passing shots on the run. Volleys can be hit down the line when a large area of the court is open (when the opponent is off the court or isolated on one side of the court).
This idea can be applied to doubles by hitting the approach deep and down the middle, and then covering the middle. Use the crosscourt or angle volley to win the point.