Most professional matches have points that follow certain patterns.
After the serve and return of serve, many players use a few cross court groundstrokes to get the opponent moving and open up the court. Very often the point ends before any other strategy is implemented. If the point lasts past the first few hits, it sometimes is difficult to decide when to change the direction of the shot.
Human nature is to hit the ball to the opening-the opposite side of the court from where the opponent is currently standing. However, this could mean that you are changing the direction of the shot on almost every ball, depending on where your opponent's shots are going. My advice is to keep the cross court direction going until you get a ball that is comfortable to hit down the line.
Try to pay less attention to where your opponent is standing and make your decision based on the type of ball you are dealing with. It will become more and more obvious which shot to select as you see the result of your shots.
Keep in mind that it is easier to hit the ball to the area from where it was hit, instead of changing the direction and hitting to the other side of the court. It is better to hit the ball well, rather than changing the direction and not executing the shot as you had intended.