It is good to wear your body suit while having someone to draw the stripes for you as this will give a more accurate and even looking stripes compare to just laying your suit on a flat surface. And again, a little heat is needed to dry the stripes. It is best to use a hairdryer.
One more thing to consider is the price of the things that you need to make your own Avatar costume. These can range from medium to expensive. It is good to do price checking before you start making one.