You should choose a location where your plant will get as much sun as possible. You also want a location where you can till all the way around your blackberry patch. Blackberries, like all brambles, will try to expand their domain. The soil should be well tilled and free of weeds. You should dig the hole about twice as big (width and depth) as needed and then partially refill the hole. This will loosen the soil and allow the roots to expand more easily. Then you plant your blackberries to at least the same depth they came in. You can plant them an inch or two deeper. I like to add a couple of inches of pine straw over the entire patch. That will help suppress the weeds and still allow the new canes to pop through nicely. Water your plant in, and you are all set. If you want to use some water-soluble plant starter, that may give your young plants a boost. I use Southern Ag Plant Starter.