Step 1: Materials needed
Don't stop there though - go crazy decorating! Add jewels, appliques, iron on transfers - or as this instructable shows - screen printed floral border.
For screen prints you can use any type of t-shirt material. For iron on transfers, I have found that 50/50 t-shirt material is the best. Cotton tends to have too much "moisture" within it that the ink does not adhere well.
When in doubt, read the instructions on whatever image process you are using.
Step 2: More advice
If you're using iron on transfers - make sure you're using a white or off-white t-shirt. Iron on's will not work with most other colors. Even if you're screen printing - make sure you're using OPAQUE inks for darker colors.
Again - read the fine print for the medium you're using.
Step 4: Cut out the "dress"
Step 5: What length do I need?
If you are using my pattern - just move it up or down the length of the t-shirt. Use the t-shirt hem as your hem - no need to have extra sewing!