Starting perennial flowers from seed is much like any seed starting, except that many won't bloom until their second season. Since they are gong to be around awhile, during their first year perennial plants put their energy into growing roots and storing food. Still, it's a great way to add inexpensive and unusual plants to your garden.
You can start perennial seeds in either late summer or fall, indoors in the spring, or direct seed in the spring.
Sowing in late summer or fall will give your plants a head start on the following season. They will have all winter to continue growing roots and they will be ready to bloom the following year. However they may need some winter protection.
When starting seedlings indoors, treat them like any other seed and move them outside, after your last frost date. Harden them off, before planting.
Direct seed plants that don't like having their roots disturbed, like poppies, or seeds that need a period of cold to germinate, like Lupines, in early spring. Be sure to mark the spot, so you don't think they're weeds, and keep the area moist while the tiny seedlings mature.
If you have the space, perennial seedlings can be kept in a separate nursery bed, where you can keep an eye on them and pamper as necessary. At the start of their second year, you can move them to a permanent spot in the garden... and start all over again with new seedlings.
Keep in mind that a lot of newly introduced perennials are hybrids and won't grow true to type. These plants will have to be propagated by division, not seed. However, if a company is selling seeds of a perennial, you can rest assured that those seeds are open pollinated.