Learning to make sets of things can be daunting. To throw the same form over and over again with precision takes a certain amount of tenacity. When a home furnishing store commissioned me to do a set of custom tumblers, I readily agreed, like I knew how to do that. At first, each tumbler took me about half an hour to make, hardly cost effective. But I persisted, cutting and throwing away more than half. Gradually I improved, and reduced the clay weight for each tumbler by 1/4 pound. Now I can throw them easily and quickly, and I am a better potter for enduring the process.
Pick a time when you have a couple of hours to throw without distraction. Consistency in all aspects is the key. Measure everything! Have a notebook to write down all of your measurements, and keep the notes for future orders. Start by wedging up the clay you want, precisely weighing each chunk, and wrapping them in plastic within reach of your throwing area. Start with at least 8 balls of clay. Have all of your bats also within reach. Center your first ball, and measure the width that you center it to, as you want to do each of them the same. As you open it up, measure the thickness of the floor with your needle tool. A fraction of an inch difference in floor depth can throw off the consistency of the pieces. If you use a rib for throwing, use the same one for every piece, as the shape of the rib influences the shape of the pot. Measure the final width that you open the pot to, and do each one the same. Finally, measure the height and width of the finished piece. Finish the rim of each one the same, and trim each foot the same, taking measurement of the foot width. Even with painstaking efforts, there will be some variation in your pieces, they are handmade! By glazing them all the same, you can minimize these variations.
The repetition of making sets can be both soothing and annoying depending on your mood. Nothing will improve your skills more, though, so stick with it!