Our top piece of advice for cropping is to always upload images cropped to the dimensions you're ordering, but we've also put together some tips for specific products below.
Proof Print Cropping
Our proof prints offer 1/4 or 1/2 borders which affect the printed image's aspect ratio. For example, if you order 4x6 proofs with a 1/4 inch border, you will need to be sure to crop your images to 3.5x5.5 to ensure that the image is cropped to your liking. Simply double the border size and subtract from each dimension to find the crop you need.
If you'd like to print an image using a different ratio, be sure to add whitespace to match while taking the selected border into consideration.