No, email isn’t the best way. Just follow the order process – place and pay for your order first and when you are at your order confirmation page you can use the uploader on the page (which can also later be found on your order via the ‘My Account’ link at the very top of every page).
This way your images are tied to your order, plus you can review your images as you upload them.

You can also use our WeTransfer service if you prefer:
WeTransfer uploader