If you already have the basic stokes down, beernutz has great advice above to use the machine to work on your footwork.
In competition, players hit to the open court.
So start from a neutral postion, and run to the spot the ball machine is hitting the ball to, and recover as quickly as possible back to the neutral position. Keep repeating.
Each time you refill the ball machine, slightly increase the speed /spin. By the end of the session you should be able to handle tougher balls, and keep working on this over time.
Practice hitting to a target - you will want to be able to hit both deep down the line and cross court shots, as well as angled shots.
As beernutz said, work on running to volley the ball to develop your all court game,
Intenionally challenge yourself running to hit difficult volleys and half volleys.
Shoot balls to midcourt to practice approach shots.
Every time you have difficulty in a match with a shot, make a note of it, and practice it with your ball machine. For example, you may have difficulty with someone who hits hard crosscourt slices to your backhand that stay real low.
If you have room in your vehicle, putting your ball machine on top of a simple cart you can buy from Sears or Harbor Freight will allow you to keep the ball machine closer to the baseline as you crank up the speed. (At high speed, even with topspin applied, the ball machine on the ground has to throw from quite far away.)
It is not high enough to ideally practice returns of serve, but it seems much more realistic than against a machine on the ground.
It also seems more realistic practicing your volleys.
The lower part of the cart can be used to bring your tennis racquets, balls, and water.