The key to giving yourself the best chance to win is to understand that tennis is a percentage game, and knowing what the high percentage shot is in any given situation. In practice, it's actually very simple. The winning part comes down more to making high percentage choices with discipline and then just executing your shots.
Having said that, cross court is always the primary high percentage target from the baseline. Trying to redirect a cross court shot dtl presents a few problems. (1) It goes against directionals and, therefore, has a tendency to go wide, (2) you have a shorter court with a higher net, and, perhaps most importantly, (3) unless you hit a winner (a low percentage play from behind the baseline to no matter where you hit it), you have left yourself out of position and given your opponent a wide open court cross court to your other side.
The exceptions to hitting cross court are: (1) when your opponent hits a short or weak ball, or (2) when you have an opportunity to run around your backhand and hit an inside out, or inside in forehand. Obviously, what amounts to a short weak ball, or an opportunity to run around the backhand, changes as the level of play goes up. For a low level player, a short weak ball is when he's closer to the service line than the baseline. For a pro, it's when he can take a ball inside the baseline. For Federer and Nadal, it's any ball that doesn't put them on defense. Anyway . . .
On a short/weak ball there are two scenarios: (1) If the ball is a high sitter, it is a high percentage play to go for a winner into the open court. (2) If it's low, and you have to lift it above the net, going for a winner (other than a drop shot which is a good option on a low short ball), is a low percentage play because it's too difficult to hit up over the net, and get the ball back down inside the court, with enough pace to be a winner. Rather, on low short balls you should hit an approach shot dtl and position yourself at net so that you take away a dtl pass attempt and force your opponent to go for a cross court pass or lob. He only has a small window to get the ball by you cross court and keep the ball inside the sideline. Those percentages favor you. For every successful pass, he'll hit at least one UE and one shot you can volley away. A cross court approach shot is a tactical error because you have left yourself open to be passed on either side, the open side and behind you as you scramble to cover the open side.
When you run around your backhand to hit inside out, you are in effect hitting cross court with your stronger stroke and only a little bit out of position. Hitting inside in is going with directionals, but, its the short court and the high net and will leave you out of position if it isn't a winner or at least puts your opponent on the stretch so that he can't hit big to your open cross court.
That's a major part of high percentage tennis right there. Hope that helps.
PS: According to Vic Braden, the average pro point lasts for 3 shots in play, serve, return and one more shot in play before someone hits an UE or a winner. For amateurs it's 2 shots in play, serve and return. This is why I say that the majority of your practice time should be devoted to: (1) serves, (2) returns, and (3) cross court drills. The point is, it's important that you know you can hang with anyone hitting cross court on either side for as long as it takes to get an opportunity to attack. There's no excuse to be stuck with a weak side that you can't hit cross court for as long as it takes. Trying to get out of it with a low percentage shot selection is not a winning tactic in the course of a match.
