When shopping on this site, get familiar with upcoming preorders that will be published as 'coming soon' products on the website ahead of time. Then, when checking out, the best way is to use the Shop app from Shopify because it lets you store all your payment settings and addresses ahead of time for quick check out. If you don't want to use the Shop app but still want a faster check out experience, you can also pay via PayPal.
If you're looking to join a Group Order (GO) for your country, check the Current Group Orders page, contact the GO for your country, and check if there's an available preorder slot. :)