了…就 / 了…再【le … jiù / le … zài】

了 after the first verb says that action is finished before the second one starts. 就 or 再 before the second verb links them: "after X, Y". This 了 marks completion, not past time, so the frame works just as well for tomorrow.

就 or 再

就 says Y follows straight after X, with no delay, and works for past, future and habits. 再 says don't do Y until X is done; it looks ahead, to plans and requests.

When the second action is in the past, 再 doesn't fit. Use 就, or 才 if it happened later than expected.

• × 昨天我做完了作业再睡了 → 昨天我做完了作业才睡
• × 他到了家再给我打电话了 → 他到了家就给我打电话了

Where 了 goes

了 sits right after the first verb, before its object: 下了课, 吃了饭. With a complement, it follows that: 做完了作业.

先…再 sets out two steps in order without stressing that the first is done; 一…就 stresses that the second follows instantly.