Getting a blue spandex (Lycra) body suit is the first step you should take. Often referred as zentai suits, these suits are easily available in different local stores. If the suit is not available in nearby market, you can easily buy it online. Just go to Google, and you would find plenty of stores offering these suits.
After getting the suit, it is time to paint blue stripes on it. Since the suit is already blue, you must ensure that the colour of the paint is slightly darker. Use a brush, and paint stripes down the back, arms and legs.
After painting the dress, it is the time to make the tail, which is a very important part of the costume. It should be made of cloth. Find a piece of cloth that is similar to the colour of the suit.
Make a tube of the cloth by sewing it. Put in whatever you want, but the pillow stuffing is the best thing to use. Make sure the tail looks just like the original one.
The next step is to make a loin cloth. Use a few pieces of fabric for this. You can always use earth tones to match the Na’vi.
If your suit does not cover the face, you should paint your face to be like Neytiri. For this, you should use blue face paint. Make sure no skin is showing through.
Now move up, and work on your hair. You have to be very wise in this step, because the Na'vi have a very distinctive hairstyle. Those who don’t want to have their hair braided can leave them anyway, but it may reduce the charisma.