Think about how you use your lawn. Is there an area where the kids play, or where you like to walk, or where for other reasons you need a fairly durable vegetated surface? Turf grasses are unexcelled at this. But if your yard is like most suburban yards, there’s a lot of grass that isn’t walked on much; some of those areas are good candidates for conversion.
Another area to consider is underneath trees. Grass growing right up to the trunk isn’t particularly good for the tree; one arborist we know has a saying, “healthy lawn = unhealthy tree” because of their differing needs for fertilizer, water, and pH. Many arborists suggest mulching out to the tree’s drip line. One concept that has been gaining traction, known as Soft Landings, is the planting of native plants underneath native trees, particularly those like oaks that support a lot of insect species. Many of the insects that feed on trees drop to the ground to complete their life cycles in the soil and leaf litter, and often perish on the compacted, mown surface of lawns. (It will be important to leave the leaves for them to survive).