You had better buckle down!

你最好多用心！

We must buckle down ourselves until we complete the tower.

我们必须全力以赴直到我们完成了这座塔的兴建。

He'll have to buckle down (to his work) soon if he wants to pass his finals.

如果他想通过期末考试就必须马上下苦功。

It focuses them and makes them buckle down and do the right things in life, he said.

它的重点，并使其成为扣下来，在生活中做正确的事情，他说。

You can follow your dreams someday, but right now you need to buckle down and be responsible.

你可以以后再去追逐你的梦想，但是现在你必须铆足劲并且负责任。

Vagner: No, you can't do that. You have to buckle down and learn what's in this manual. I'm here to crack the whip.

瓦格纳：不，你不能那样做。你必须全力以赴，学习手册上的知识。我就是来鞭策你的。