Look up information about the bush you are using to find out how wide it normally grows.
Plant the bushes so that the width of the grown bushes will meet and overlap a couple inches. For example, if a bush will grow to a width of 3 feet (1-1/2 feet on each side of the trunk), then the space between the two shrubs should be 2-1/2 feet.
Trim the side branches of the bush during late winter before it is time for new growth. Only cut a small 1- or 2-inch portion off of the branches. You want to encourage growth of the side branches, not trim them back. Make cuts at a slight angle just in front of a leaf or fork. Once you get the shrubs to bush out on the sides and grow the extent you want, then you will no longer trim the sides in the late winter. You change to just the summer after growth has formed.
Cut the top of the bush to start forming a uniform flat surface. Allow the bush to grow upward until it reaches the height you want the hedge, but keep the branches trimmed evenly.
Snip the ends of the side branches again in late summer so that they are encouraged to grow again. Do not wait until fall, or the new growth won't have time to harden before winter.