See the wikiHow article How to Knead Clay
You may get thin or weak spots as you roll your coil out. Try avoiding that section as you work, but if it becomes a problem just break the coil at the weak spot, set one part aside, and finish the other.
You can also create the bottom by rolling out some clay to about the same thickness as your coils, and then trim the excess with a knife, using cup or plate as your guide.
To maintain the shape of your pot, support the outside of the pot as you smooth the inside. [2] X Expert Source Natasha Dikareva, MFACeramics & Sculpting Instructor Expert Interview. 5 May 2020. You can smooth both inside and outside if you wish.
You can tell the clay is centered when it no longer looks like it’s wobbling, but sitting stationary in the center of the spinning wheel. Don’t stop spinning.