First come, first served.
First things first.
One German translation would be “eins nach dem anderen” — one thing after another; break it down. The other would be “das Wichtigste zuerst” — the most important thing first; prioritize. I don’t think there is an equivalent phrase with both meanings in German. Wow: yet another example of how much we leave unsaid and up to context in English, whereas you tend to spell things out in German.
Trying to get through deadlines and Christmas preparations, maybe you’ll enjoy this cute little motivational sketch as much as I did.