This was my first really successful foot on a piece. And it took a good deal of practice to get there.
First, I had to get really good at creating a centered piece. Once I had that, making a good foot became much easier.
Second, I learned when the clay was ready to have a foot carved into it. Not too dry and not too wet. The advice I got was to wait until the clay was the consistency of grocery store blocks of cheddar cheese.
Third, just getting the feel for where the foot went was key. (It should be just under the part of the piece where the sides start to rise). This guide from Lakeside Pottery is very helpful.
Finally, the foot trimming process was tricky to get down. Watching videos helped a lot here. I recommend:
And lots of practice. The thing that finally got me on the road to success was having nice sharp tools and speeding the wheel up.