A beautiful and more deft way to design a garden is to plant in a more naturalistic way by interplanting different species. While it can be visually arresting to plant a block of say, Culver's Root, variety really is more interesting. And it's true that some plants form larger contiguous spatial blocks as they grow because they're rhizomatous, using modified stems that grow at or under the soil surface and spread horizontally (e.g. Wild Bergamot), so to some degree interplanting different species together is easiest with clumping plants. You can accomplish spatially mixed plantings that include rhizomatous species, too, but it just requires more editing to maintain it.
Practically-speaking there are a few ways you can end up with this kind of garden look. The first involves scattering a seed mix of multiple plant species on a patch of soil, which is a fun way to do it because you don't know exactly how it will turn out and which species will turn up where. The advantage to this route is that the plants that take to a particular spot often thrive there and they continuously grow their root systems without interruption. A note of caution though: this strategy can sometimes yield no results if birds eat all of the seed. We've experienced this firsthand. Not the worst thing in the world (congrats on providing forage for them), but it makes for very expensive bird seed! You can place a cloche (cage) on that patch of dirt or set up sections with boards and chicken wire covering them to prevent that from happening.
The most deliberate method though is to either grow seedlings from seed or order from a nursery and transplant the seedlings according to your design. The benefit here is that you can be reasonably certain what it will look like, at least in the near to medium term. Even with transplanting it's always good to be flexible because certain species may not establish as well as you would like for the specific locations you have selected. Transplanting also generally involves some shock to the plants as they adapt to their new home, meaning they may grow more slowly in the short-term. But transplanting is the method we have generally used for introducing new species to the garden and with quite a bit of success (and some failures for sure!).
The last technique is one of our favorites and requires you to step back, to be less controlling, and not be stubbornly wedded to a design: allowing volunteer plants to grow where they come up. In fact, every plant in the foreground of the picture above is a volunteer plant that we did not intentionally plant! This is not to say that you let them come up in terrible spots that you know they will struggle in, but it does mean letting your garden evolve in ways you did not originally intend. This route is obviously an easier option if you have already established some amount of plant diversity in the garden. Seeds from those established plants will wind up in unexpected places. But we have also had some species show up without us ever adding them intentionally. Late Boneset fits into that category. One day we noticed it growing in several places and decided to be patient and wait to see what came of it, which turned out to be the best decision we could have made. It rapidly became one of the best plants in our garden for fall pollinators, Monarchs included.