What should I add to my soil before I plant?
Adding compost is the best amendment for improving soil conditions. The City of Edmonton has a very good course on how to properly compost. They also offer expert advice with a composting coach.
Most potting mixes are blended for pots to avoid waterlogging. Never use soil straight from the garden. If the soil is composed mostly of peat moss, it can dry out more quickly. By adding a small amount of compost it will improve water retention.