Find Your Opponent's Weakness
Quickly identifying and honing in on your opponent's weakness seems obvious. However the majority of players don't. With most levels of players, an opponent's weakness is their backhand.
Aim to hit more than 70 percent of your shots to their weakness, until the court opens up to attack their strength if need be. Even if 70 percent is unattainable it will still create the right attacking mindset.
Rafael Nadal won his first Wimbledon against Roger Federer in 2008 with this basic tactic, hitting a heavy-deep ball (off his forehand) into Federer's backhand. It wasn't rocket-science and it won him the greatest title in tennis.
Notice he used his strength against Federer's weakness. You're aiming to do the same thing. If you're hitting your backhand into their backhand (assuming these are both the weaker shots in both you and your opponents game) then it's just an even playing field. Hone in on their weakness with your strength.
Allow For a Margin of Error
The pro's respect the fact that they never quite hit their targets. They allow for margin-of-error over both the net and within the lines of the court. Focus on this, especially when in a defensive situation, aiming to hit deep and down the middle of the court. Tennis Drills HQ has a great drill for practicing this.