Sketch out your design ideas before creating the actual costume. Shade in various colors on different areas of the costume sketch to compare tones and visual qualities. Write out a thorough supply list so you can purchase or gather from your house everything you need at one time.
Lay out a long-sleeved shirt and pants onto a flat surface. You can choose any color for the shirt as long as the pants are the same color. Cut out pieces of faux fur and glue them on randomly over the front and back of the shirt and pants. Create a patchwork design to resemble different textures of alien skin. Cut the fabric in various shapes and sizes for added effect.
Wrap a pair of green pipe cleaners on opposite sides of a headband to make alien antenna. Glue Styrofoam balls colored with markers onto the pipe cleaners. Add pinches of tin foil or metallic paint to make your antenna sparkle.
Cut out long strips of satin or polyester fabric and glue them to the underarm side of each sleeve. Attaching long strips of fabric gives the costume draped, alien tentacles. You can also used safety pins instead of glue to attach the fabric strips.
Get creative with your face paint. Choose face paint colors that match the fabric of your alien skin. Outline your lips and eyes with an eyeliner. Dot your face with an eyebrow pencil for alien freckles . Add spacey-shapes such as zigzags and spirals, and sprinkle your forehead and cheeks with glitter to complete your face paint.