Clay color is critical to deciding what color to paint your flower. If you choose a darker-colored clay, like red, and you want some of that color to show through the mold, choose a lighter hue of red to complement the clay's base color. If you're just using paint for the color of the mold, pick a lighter-colored clay, like white or tan.
Use acrylic paint for your clay molds, as they don't react negatively with the clay. Mix the pure acrylic paint with water to dilute it slightly: two parts paint and one part water is ideal. Creating this solution makes the mold smoother to paint and allows for more mistakes, as the paint isn't as strong per brushstroke.
Have a few different kinds of paintbrushes available. A liner paintbrush allows you to paint very small details, like those found in the center of the flower. Flat brushes are good for covering the first layer of paint in broad strokes. Use fan brushes for wider surfaces, such as oval petals of a flower. Have at least one of each type of paintbrush. Different sizes of these paintbrushes prove useful, too. Use a small palette for your paint.
Choose what kind of flower you want to paint, knowing you'll need an assortment of colors. The base of the flowers will be colored differently than the stem and leaves. Details on the inside of the flower will need a finer brush for a different color. Paint the base of the flowers first with one coat, using a wider brush like the fan brush. Paint the leaves green using the same method. After laying down the base paint, use more stark colors on the inside the flower with the liner brush. Once the details of the flower have dreed, apply a second layer of lighter-colored paint to base areas to add depth and texture.