One of the first pieces of advice that a coach provides his/her student is to not aim for the lines when playing points. The concept is fairly simple to understand in that the developing players are relatively inaccurate when it comes to their strokes so there's a chance that aiming for the lines will result in the dreaded "unforced error" [GASP!!!]. So with this advice in mind, the players end up trading blows aimlessly from the middle of the court until, usually, the steadier player runs away with the match. Nevertheless, this strategy is risky down the road since, if the player remains stuck with the mentality that she is supposed to hit away from the lines, her shots are going to end up landing in the middle of the court where they are easily accessible by the opponent.
Therefore, as the players get older and better, it is important to attempt to transition away from the "stay away from the lines" mentality to a "stay just inside the line" mentality. Yes, this will require a lot of focused and, sometimes, frustrating practices. However, if you are unable to get the ball away from the middle of the court - be it with pace, height, spin or angle - chances are that a better "ball striker" will chop you up and "T off it" as soon as she gets the chance (which, generally, means the 2nd time your shot lands in/around the same place).
It is amazing to see how, sometimes, juniors never seem to realize when their shots are landing smack in the middle of the court - and, by extension, within the opponent's strike zone - 3, 4, 5 or 6 times in a row. What are they thinking?! They either (a) don't know what's going on; or (b) know what's happening but are afraid to miss. Here's a way to fix it: set up a square that is 3ft x 3ft from the service T (use athletic tape). Initially, play a baseline game (or, better, a game with one serve) and see how many times the player hits the ball inside that square. Thereafter, play a game where the player automatically loses the point if the ball lands inside that square. As the player gets better, expand the size of the square (blue - purple - red) until it's 5ft, 4ft and 3ft from the sidelines. As the player improves, he will become more and more comfortable hitting the shots "just inside" the lines. The goal is for the strokes to be as penetrating as possible and, at the same time, have as much control as possible. As one of my team-mates (Freddy Giers) used to say, "you're only as good as your worst shot on your worst day". The objective here is to become as steady as possible while also being as dominating as possible.
In the second diagram, the object is more or less the same although the "red zone" is a no-hit zone while the "blue areas" are the automatically-win-the-point areas. As above, the purpose of this game is for the player to develop (1) awareness of his shots, and (2) confidence in his strokes and his ability to move the ball around as much as possible without either forcing or missing.