I think you should…

“我认为你应该做某事”，这就是很直接的提建议的方式。

Maybe you should try…

“也许你该试着做某事”，建议去做什么。

If I were you, I would…

“如果我是你，我会怎样想怎么做”。

My advice is to…

“我的建议是”，很直接的建议。

He's a bit of a bully and my advice is to have nothing to do with him.

他有点霸道，因而我的意见是不要和他交往。

Why don't you…?

“为什么不”，提出建议。

Why don't you wear shoes with high heels?

为什么你不穿高跟鞋呢？