Pull out the old planting, including all the roots. This gives any new plants a clean slate for growing. If you're dealing with an outdoor garden site, remove any weeds and rocks as well.
Dig into the top 6 to 10 inches of the site and break up compacted, old soil. This aeration is the first step in rejuvenating soil. If you're reusing potted soil, dump the soil into a bucket or bin for new mixing.
Turn 3 inches of organic compost into the top 6 inches of soil in an outdoor garden to boost the soil's nutrition, drainage and moisture. If you're remixing potting soil, add compost until you have a mix of 1/2 old soil and 1/2 new compost. This amendment gives old soil new nutrition, and increases the quality for new growth.
Mix granular 13-13-13 fertilizer into the top 4 inches of an outdoor site, and throughout the soil for potting soil. The fertilizer gives long-term, slow-release nutrition for new growth. Water the outdoor site for 10 minutes to settle the soil and fertilizer, and water potting soil until it's moist, for the same reason.
Reuse the soil for planting, as you would use new soil.