There are a number of ways to sample soil in your fields. The bottom-line, you are trying to get a good indicator of the soil nutrients in your field and find places where the nutritional levels are vastly different. With GPS technology, soil sampling has become very sophisticated with respect to defining your field. I do like to revisit soil sampling processes from the past few years and look at ways to get a better picture of my own fields.
I came across this video on grid sampling and zone sampling. It really does a great job of defining and showing the process. Sometimes, it is good to take a few minutes and getting some ideas for soil sampling. Check out this video from the Ag PhD series.
Photo provided by Northwest College Agriculture