Pressing images onto a zip up hoodie, I recommend:
1. zip up the hoodie and lay it out on your table.
2. cut the design in half where it needs to be separated for the zipper. If the actual design needs to get cut in half, you should cut it with your program before you plot it.
3. Lay out your design in the appropriate location, and secure with tape on the top and the bottom.
3. Take your pillow that you use, and put it half way on the press (leaving half off).
4. Take your hoodie, and place it sideways on the press with the zipper right at the end of the pillow. Ensure that the sleeve up by the shoulder is pulled out and not interfering with the tight press.
5. Press the first side.
6. Take the hoodie off the press, rezip it (be careful, the zipper will be HOT) then align the other side of the design on the other side. Tape it then follow the same process to press it.
I found this is the easiest way to get the most even press.