Often, the petals will glow with beautiful iridescence. Backlighting is often the best type of lighting for translucent subjects like petals. However, don't despair if there is no sun. Gray and overcast days provide great opportunities for flower photography. The lighting is more even and there are no shadows.
Rain turns colors more intense.
You can even carry a spray bottle to create rain droplets on the sunniest of days. Even night photography is an option. You'll be surprised at how attractive a flower photo can be when illuminated by flash. Second, to make a flower picture come alive, wait until something adds life to the flower - for example, a bee alights, or a spider crawls into it, or a hummingbird pays a visit. It takes patience, but it pays off if, for example, after you wait a few minutes, a butterfly lands on your flower.