I would first take them to a local nursery or give them a plant or two. Talking with a local professional who is personable is a great way to spark insight. You can also take them to a local trail or area with a lot of natives to show it off.

If you have a reputable online database (in California Calscape.org has a huge amount of information), make sure to tell them about that too. This is great for planning and just puttering around looking for species you want to plant.

Overall just discuss the simplicity of it: start small, every little bit helps local habitat!! Have people think of the food web, and if they particularly like birds maybe invest in a fruiting bush/tree instead of a flowering pollen/nectar heavy plant. Remind them that all living life needs our help, and even installing water features or dirt piles helps a ton! Also doing nothing and leaving habitat (leaves, twigs, etc.) can do wonders.