Watching the ball is the most important point of focus when trying to hit a tennis ball well. It is a necessity if you are striving for that consistently solid hit.
Your line of vision is something that is rarely mentioned, but equally as important. If you can focus on the area to your right or left at approximately a 45-degree angle when you are about to make contact, your chances of hitting the ball squarely in the center of the strings will dramatically increase. We tend to look towards the opposite side of the court too much, too often and too soon.
Another common problem is trying to go from watching the other side of the court to the expected point of contact, and often missing that 45-degree point of contact area. I have many students who are looking directly sideways (90 degrees) and making contact late. By following the ball from your opponent's racquet to the 45-degree area, and keeping your focus on that contact point for a fraction of a second longer, you are encouraging an early hit, helping your body stay under control, and also enabling a quick recovery as you watch the ball with your peripheral vision leaving the racquet.
Keep in mind that you are unlikely to actually see the ball leave the racquet since everything is happening so quickly these days on the court. However, you will be able to pick up the ball sooner as it is traveling towards your opponent's side of the court.
Use the 45-degree line of vision to help get a solid hit and improve your recovery and reactions.