Spacing from the start is good. Alternatively, at least when starting from seed, my approach is usually to plant densely, and thin things out as plants grow so you can select the strongest specimens.

Admittedly I've got more experience with vegetables and herbs than I do with flowers. I know whoever owned my house before me struggled horrendously with the idea of spacing though; I've got half a mind to buy a flamethrower to address the "garden" at the front of the yard.