Start with a thorough soil test.
Organic matter is always a good plus. Look at a green manure suitable for your region too.
I like a green mulch to build the bacterial soil organisms. This year I planted half my home plot in rye to use as a mulch; a good allelopathic treatment to control weeds while the plants grow.
Build a compost or find a source of cured compost. The leaves are agood fall addition.