The first step in tie-dying is figuring out what pattern you want to create. For this American flag pattern, I folded the shirt in a diagonal pattern.
Once folded you can rubber band the shirt so that the dye won't bleed.
The first part will be wider to create the blue portion of the flag and then the others will be spread apart evenly. See pictures on-site if needed!
Once you have your shirt rubber banded you are ready to start the process of tie-dying.
I actually used a spray bottle style so it wasn't as messy for me. If you are using a bottle of dye I would suggest putting your shirt on a rack so the dye won't puddle and bleed through to the other parts of the shirt.
Allow your shirt to dry fully. Most likely overnight would be best.
Then you can cut off the rubber bands and heat set in the dryer for 20 minutes.
Once heat-set you can wash as normal.
Notes
I would wash it by itself for the first couple of times just to be on the safe side.