When I was over at Deer & Deer Hunting, there was a group of guys who were big fans of natural ground blinds.
Everybody had their own school of thought, but generally speaking:
1) Get in early, and do it. Start in the spring at least getting the big pieces dragged in and set. Deer are hinky about stuff that shows up in their environment.
2) Most of the best blinds come from being up top looking down. You want to see and not be seen. The higher you are, the less likely you are to be smelled. The heads and sides of ravines are the best.
3) If you build it right, a blind can last decades, but it will require brushing in every year.
4) Stillness is the key. You have to be able to be absolutely still
