Plant milkweed! They seem to like butterfly milkweed more than common milkweed when I look around the neighborhood, but YMMV. Common, swamp, and butterfly milkweeds are the best choices.
There’s a certain critical mass of milkweed you need before the monarchs will lay eggs on them. Doesn’t have to be a huge amount, but one small plant won’t do it. Also have some other plants and things nearby where the chrysalis can hang. We’ve yet to find any chrysalis despite 20 some caterpillars last year.