先…再【xiān … zài】

先 marks the step that comes first and 再 the step that follows. Both are adverbs and go right before their verbs. The steps belong to something that hasn't happened yet – a plan, a suggestion, an instruction.

再 goes after the subject

When the second step has its own subject, the subject comes first and 再 follows it.

• × 你先走，再我走 → 你先走，我再走

Not until

先…再 often says the second step waits for the first to be done – "only after", "before".

再 or 然后

然后 also means "then", and it narrates events that already happened. 再 stays with what is still to come.

• × 昨天我先去了超市，再回家了 → 昨天我先去了超市，然后回家了

This 再 is the same word as the 再 that means "again"; here it means "and after that".