The good news: You don't have to!
OrbitKit has smart algorithms which inspect your artwork and place it tastefully in the print area of each product - big and centered. You should not need to manually adjust anything.
If you are unsatisfied with the results, or are looking for some sort of special behavior, reach out to support. We can always make the algorithms smarter!
Some things you might want to know:
You can take over positioning. If your artwork conforms to the Amazon Merch format (4500x5400 pixels), we disable the automatic positioning code for most apparel. Your artwork will be used as-is, with spacing determined by your transparent borders (just like Merch). Note that this only applies to products with tall/narrow print areas; hoodie fronts are adjusted to landscape orientation (if possible).
You have one input into the positioning logic. "Art Size". There are two values:
STANDARD is the usual smart OrbitKit positioning.
MAX will make your art as big as possible on the product, to the edges of the printable area. This will bypass the Merch-format positioning, eliminating the transparent space in your image file.