Ask HN: When outsourcing development, front end UI or back end first?

Non-technical solo founder outsourcing development on a MVP web app (but also learning basics of coding in the meantime in order to better navigate the process).

As for the question: I realize that it is an iterative process and that development of each end doesn't happen in isolation. But in terms of practical application, you have to start somewhere and one part has to take the lead. What's the most common approach? Any reason to take the less common one? Is one better suited when outsourcing?

Any practical advice or tips much appreciated.