'You'd' is a contraction of 'you had' or 'you would.' You are making a suggestion to someone for a particular action.

'You'd'是'you had'或者'you would'的缩写形式，你是给某人特定的行为提建议。
Here are some examples: 这里有一些例子： 

"You'd better exercise."

 你最好锻炼一下。

"You'd better help out."

 你最好帮帮忙。

"You'd better invite your brother."

 你最好邀请你的弟弟。

"You'd better impress the judges."

 你最好给评委留下深刻印象。

"You'd better listen to your parents."

 你最好听你父母的。

"You had better not come home late."

 你最好不要晚回家。

"You had better hope for the best."

 你最好抱最好的希望。

"You had better change your attitude."

 你最好转变你的态度。

"You would be good at teaching."

 你会擅长教学的。

"You would do well at math."

 你的数学会好的。