Weekend players frequently make a big mistake in court strategy: they fail to capitalize on their opponent's short shots.
A short ball gives you the chance to move up to the net and establish a command post from where you can volley away the next one for a winner.
Good tennis is a matter of closing out the point, which in its most obvious form means taking control of the net. You can do that by being ready to move in for a short ball and pouncing on it. Return it so you can pin your opponent well back in his own territory.
Play a step or two inside your own baseline to give yourself a head start. Don't worry about being caught by deep shots. The average player is average, after all, because he seldom drives the ball deep enough.
Always be alert to the chance to jump on a short shot.