It's tempting to think of nurturing soil activity in terms of what microbes you can add to the soil. Sometimes, however, it's simply a case of conditioning the soil in such a way that microbes take care of themselves.
Like most life forms, fungi and bacteria require a few simple things to thrive—most notably they need both water and air. Oddly enough, improving drainage in soils by adding organic matter actually helps provide both, ensuring a porous soil structure that retains water but also contains air pockets and lets excessive moisture drain away.
Peat has traditionally been the soil amendment of choice for improving drainage, but peat is a non-renewable resource and is also fairly acidic. Coco coir, the fibres from coconuts that are often considered a waste product, is considered by many organic gardeners to be a more sustainable and possibly superior peat substitute. Nature's Footprint is just one company offering coir bricks for use in gardening:
By adding one part coco coir to two parts soil or potting mix containing compost, you can make a perfect growing medium for container or potted plants. You can also mix one part coco coir to two parts top soil in an outdoor garden or raised bed to improve the water holding capacity and structure of the soil.
Speaking of healthy soil, another company, RoLanka, offers coir mats that are used to control soil erosion.