The perfect garden mix consists of several different ingredients to help your plant's roots breathe, absorb water and nutrition. In general, garden soil has more nutrition than all-purpose potting mix.

Soil
This part, called soil, often consists of clay, silt, peat moss and organic matter. Should be around 50% of the content in a good all-purpose garden mix.
Compost/Nutrients
The compost helps the soil retain water, improving aeration, controlling the soil's temperature and it might also provide nutrients, depending on what organic waste was added. Nutrients/fertilizers that dissolve slowly are preferred. This part should be about 25% of the mix.
Sand, Perlite & Vermiculite
Improves your soil’s drainage and aeration. This should be about 25% of the mix.