‘Feed your worms and soil microbes’ has consistently been the best advice I’ve found to give people in terms of soil improvement and productivity, for both vegetables and fruit trees. A layer of compost followed by mulch (anything from straw to wood shavings to tarps, at times), to keep moisture in the top 6 inches of soil and keep it active, is the best way to solve many soil issues.

Past that, leaving roots of previous seasonal plants is also very helpful. Just cut them off near the surface and shred the tops into your compost system.

Monitoring and mildly amending soil pH can also be important, but usually less so.