As usual, test your modules, your themes, your custom work (including your overrides), and if possible test it with data from a real shop.
A lot of work as been done on the Order page. Please take time on this important part too. If you are an agency or a freelancer, ask your merchants to check it with a copy of their data and/or fake orders, on a testing server. If you are a merchant, please try the order page on a testing shop.
If you find problems, please report issues on GitHub. If everything is fine for you, report it too: use social networks and groups, posts on the forum.
Read the release note and download it on the Build blog