3. Hitting to your opponent: At every level of tennis, the easiest direction in which to hit the ball is the direction from which it came. This is one of the main reasons players tend to hit back to their opponents. We also tend to hit toward whatever we're most focused upon. By far the most conspicuous thing on the other side of the net is your opponent, so your attention, and thus your shot, tends to be drawn in that direction. To overcome this, try to focus your eyes on the ball while visualizing target zones on the court.
4. Not attacking dinky serves: Against many opponents, the easiest balls coming your way will be second serves. Inexperienced players hit truly dinky second serves that are just begging to be attacked. You can hit them hard and deep, at a sharp angle, or very short (drop shot). If you keep punishing these dinky serves, your opponent will probably start trying to hit a better one than he can, and his resulting double faults will drive him nuts. Frustration will increase his errors, giving you lots of bonus points.
5. Admiring your shot: Yes, hitting a good shot is central to tennis, but you can't rest on your laurels--at least, not right away. If you stand there watching the beautiful flight of your shot, you'll be way out of position when that beauty comes back. Generally, you need to start moving immediately back toward the middle of the range of angles your opponent could hit next. This position is somewhat diagonally opposite your opponent if you're at your baseline, and it's somewhat toward the ball if you're at the net.
