When thinking about what you want to grow, consider how much shade and sun the area gets. If it's fairly shady, you need to pick a flower that's going to be happy in that area. Also, consider how much work you want to put into your garden. That is, you can plant perennials that come back every year, but that don't bloom as much as annuals. With annuals, you need to plant them each year, but you'll get more colorful blooms that last longer.
Also, make sure the flowers you want to grow are zoned for your area. You can look up your zone online or ask at a local nursery. Some perennials to try include daylilies, pansies, irises, lamb's-ears, black-eyed Susans, Russian sage, and roses. For annuals, try zinnias, marigolds, cosmos, and sunflowers. You can also mix and match annuals and perennials for the best of both worlds.