If you have to move the bush right now, you have no other option than to simply do it, but if you can wait a year I'll recommend to prune the roots first to make a more compact root system. Simply stick a spade around the bush in a wide circle that is is roughly as big as the root clump you want to move later on. If the root system is very deep you may need to dig a small trench around the bush first to get deep enough with the spade. After a year or so (this depends on species and climate, here it would take at least one growing season) the bush will have grown a new compacter root system with many fine roots where you did the cut. In the mean time water and fertilize a little inside the circle you did with the spade to encourage the roots to stay close to the bush.
Later on when you move it, it can be beneficial to slide something under it and simply drag it to its new location. This of course is just in addition to what dyzzypyxxy(Elaine) said about pruning the top growth/shading and so on.
