Use a premium quality fabric paint like
Zimprints Permanent Acrylic Fabric Paint. Zim's highly pigmented formulation is especially made for fabric stamping and will not 'bubble' or bead-up.Before you fabric stamp a garment, practice on a piece of muslin or scrap fabric. This will help you master your technique and see if your design pleases you.
Stamp on a hard, flat surface
Smooth out the fabric
Use a 1-inch foam brush
Paint the stamp surface with long even strokes
Press the Zimstamp firmly into the fabric and lift it straight off
Continue stamping until you're finished with this side
Allow the images to dry to the touch - about 30 minutes
Stamp the other side
Wash your Zimstamps and brushes in warm, soapy water
Let the fabric dry for about an hour
Iron on the wrong side at the highest setting to heatset the images
Wash and dry according to the manufacturer's instructions
Garments or fabric made of 100% cotton or other natural fibers work best.
You may want to use a piece of foam core board under your fabric or inserted between multiple layers.
If you want two colors on one stamped image, you need to paint both colors on the stamp before stamping (use different brushes for each color)
If you change paint colors on a stamp, be sure to wash and completely dry the stamp first.
Use a Q-Tip or toothpick to scoop any excess paint out out of the stamp's crevices.
When scattering the stamped images in a random pattern on your fabric, don't worry about spacing them in any regular way.
If you want to stamp in straight rows on a shirt, start at the top. Fold the bottom of the shirt up & refer to the hem to keep your rows straight.
Always try to use black(even a little bit) in your pattern or design. Black will make the other colors that you're using seem to jump out!