He did you a good turn by resigning.

他辞职对你有利。

Well, that's my good turn for the day.

好啦，这就是我今天做的好事。

They might be doing me a good turn if they took me into protective custody.

如果他们对我进行保护性拘留，那对我可能是一件好事。

You did me a good turn, and, in this world, what is given is always returned.

你帮了我一个大忙，在这个世界上，付出总会有回报的。

If you do someone a good turn today, don't expect a thank you.

如果你今天帮了别人一个忙，别期待他会说一句“谢谢你”。