https://www.seangoedecke.com/how-to-ship/
The most common error I see is to assume that shipping is easy. The default state of a project is to not ship: to be delayed indefinitely, cancelled, or to go out half-baked and burst into flames. Projects do not ship automatically once all the code has been written or all the Jira tickets closed. They ship because someone takes up the difficult and delicate job of shipping them.
That means that in almost all cases, shipping has to come first. You cannot have anything else as your top priority. If you spend all your time worrying about polishing the customer experience (for example), you will not ship! Obsessing over UX is praiseworthy behaviour when you are an engineer on the team, but a blunder if you are leading the project. You should cherish the other engineers on your team who are doing that work, and give them as much support as you can. But your primary concern has to be shipping the project. It is too hard a job to do in your spare time.