Practice ups, downs, up-bounce-ups without a partner and up-bounce-ups with a partner to develop a better understanding and feel for the length of the racquet, sweet spot and bounce off the strings and court.
Drop/hit balls (or have a friend drop balls for you to hit) to develop technique and control over placement. Practice hitting balls cross-court and down-the-line and to the four quadrants of the court as defined by the singles sidelines, baseline, service line and center service line.
Develop a low to high swing pattern for the groundstrokes. A low to high swing pattern generates topspin and allows for better margin of clearance over the net. Topspin brings the ball down and into the court.
Hit high (four to seven feet) over the net for better net clearance and margin for error.
Begin your groundstroke rallies initially close to the net and progress back to the baseline with success (10 or more shot rallies). It is easier to handle the bounce and see the ball when hitting from a closer range. Another alternative is to hit from the same side of the net.
Serve with an abbreviated half motion to better focus on the toss, contact point and finish.
Start serving from inside the service line. Progress back to the baseline with success. Move back several feet at a time until serving from the baseline with the successful consecutive completion of five or more serves.
Focus first on technique and consistency. In progression of learning, the order of priority should be technique, direction, depth and net clearance, footwork and court coverage, spin and then power.
Do everything possible to extend the length of the rally. Judge success and improvement, even when playing points, by the length of the rally. Your initial success as a player will be marked by your ability to get one more ball in play (or by your ability to make your opponent hit one more shot). A valuable exercise to improve consistency is to require a specific number of shots to be hit (i.e. five) in a cooperative exchange prior to the start of each point.
Play a lot of tennis, take lessons and most importantly have the most possible fun on the court every time you play.