Give Them Air. Most soil organisms need oxygen to survive. To keep your soil light and fluffy, add organic matter and avoid walking around on it, especially in the spring when it's still very wet. You can introduce air by loosening the soil with a fork, but avoid excessive tilling. Keep Them Moist.
Microbes require moisture, but too much is deadly.
If given the opportunity, water will fill every air space in the soil, and soil organisms will suffocate. Drainage trenches or raised beds are a good solution if your soil tends to be soggy. Dry soil is just as problematic. Keep Them Warm. Soil creatures are most active between 70 and 80 degrees F. Remove winter mulches in early spring to warm up the soil and revive the microbes.