The most important thing that you can do is to avoid systemic pesticides containing neonicotinoids that indiscriminately confuse or kill all insects, whether they are eating the plant or simply trying to pollinate them. Avoid excessive use of weed killers that can wash away and indiscriminately kill pollinator food and habitat plants.
Leave portions of your yard wild and/or enhance those areas with wildflowers, herbs, mustards and other pollinator favorites. Monarch Butterflies exclusively eat Milkweed, so if you see ripe Milkweed pods by the side of the road, grab some and spread some seeds at the edge of your woods or amongst your wildflowers.
If you are lucky, you will attract Hummingbirds as well.