Work soil around extended roots with your hands, packing with feet will tear roots. I have read conflicting things about preparing the soil for planting. Some sources say to add organic matter like peat moss, while others say it is better not to use soil amendments. Most plants grow better in soils high in organic matter. Amend a 3-4 foot wide area no deeper than the root ball.
Organic matter improves soil drainage of excess water, while holding moisture for better growth.
Large plants can be moved as long as a good fibrous root system is present. I bought some plants on sale this fall, but don't want to plant them until spring, as the location where they are going has a large number of spring bulbs. Plants can be held over winter outside in the shade with roots buried with soil or mulch. Do not allow them to dry out. In a case like this, it may be better to use the sale plants in an area where they can be planted in the fall and purchase others in the spring to plant among the bulbs.