You're too thin. You're not eating properly...

你太瘦了。你的饮食不合理。

There needs to be a properly informed public debate.

有必要让公众在充分知情的状况下展开辩论。

He's a spoilt brat and it's about time he learnt to behave properly...

他是个被宠坏的孩子，是该学些规矩了。

They will be concerned to do the right thing — to dress properly, for instance.

他们需要注意行为是否恰当——比如说，穿着得体。