The hole placement for sewing is determined as to the style of the button and how it will be used such as providing balance and stability. Some button designs are best suited with two large holes where others are better with four. At times I find the button holes would detract from the overall look so I prefer to add a shank to the back instead. My experience with sewing helps me in designing my buttons for various types of projects.
My pdf e-tutorial "Making Beautiful Buttons", contains 20 pages of clear photos and instructions on how to create buttons that are more professionally finished. I have provide instructions on how to make your own wire shanks and attach them to the back without the need for any glue. Also included are templates you can copy and use as hole placement guides so your holes are properly spaced and centered every time.
Click on the above photo to read more about our tutorial that is for sale in our ArtFire studio.