Most players below the higher levels do not really control their shots, both in terms of direction and depth. One reason for this is they don't really get much feedback on it, and so don't realize just how little they are really controlling the ball. Another is that they aren't really aiming the ball at specific spots, instead just aiming at a general area. And another is they don't really practice this type of control.
Like most techniques, it's best to practice the simplest aspects and work your way to game-type shots. So the best way to start is to put a target on the far side of the table - perhaps a bottle - and get a box of balls and commence target practice. Start by either bouncing the ball on the table or tossing the ball in the air and either hit or loop the ball at the target. If you can't hit the target this way, how can you do it in a game, where you have unpredictable incoming balls at varying placements, speeds, heights, depths, and spins? When you are somewhat proficient at hitting the target, you are developing directional control.
Next comes depth control. Fold up a towel so it's no more than 12 inches wide (smaller if possible), and put it near the far end of the table, near a corner. (A towel makes it easy to tell if you've hit it, but you can also use a piece of paper.) Now try hitting that. When you are somewhat proficient at hitting the target, you are developing depth control.
Now it's time to do it in a real rally. Place a sheet of paper near the far side of the table, near a corner, and rally with someone. See how often you can hit the paper. When you are somewhat proficient at hitting the target, you are developing directional and depth control in a rally. Not only that, but at this point you are more aware than before of actually aiming for targets and hitting them!
How does this help you in a match? Directionally, you want to hit nearly every shot either very wide or at the opponent's middle (roughly their playing elbow, midway between their forehand and backhand). Now you can do that! You also want to mostly keep the ball deep on the table. Now you can do that! Most players do not realize how many points are won and lost not because the opponent makes a good shot, but because you give him the opportunity of making a good shot by not placing your shot, both directionally and depth-wise. Why make things easy for him?