请 before an action
请 qǐng means “please” and normally appears before the action. It works in signs, service situations, and direct but polite requests.
Qǐng zuò. — Please sit.
Qǐng gěi wǒ yì bēi shuǐ. — Please give me a glass of water.
Qǐng zài shuō yí biàn. — Please say it again.
请 does not make every command sound friendly by itself. A calm tone and a question form may be more natural when asking a stranger for a favor.
可以……吗 and 能不能……
可以……吗？ asks whether something is permitted or possible. 能不能……？ literally asks “can or cannot?” and is useful when checking whether someone can help.
- 可以坐这里吗？ May I sit here?
- 可以说慢一点吗？ Could you speak more slowly?
- 你能不能帮我看一下？ Could you take a look for me?
麻烦你 and 请问
麻烦你 máfan nǐ acknowledges that you are asking someone to spend effort. It is useful for a favor and can sound warmer than a bare command. 请问 qǐngwèn means “may I ask” and opens a question politely.
Máfan nǐ bāng wǒ yíxià. — Could you help me for a moment?
Qǐngwèn, xǐshǒujiān zài nǎlǐ? — Excuse me, where is the restroom?
Requests versus commands
A short imperative can be fine with friends or in an urgent situation, but a stranger usually needs a little context. Add a greeting, 不好意思, or a question ending when you are not sure.
Compare 给我水 (“Give me water”) with 可以给我一杯水吗？ (“Could you give me a glass of water?”). The second sentence identifies the request and gives the listener room to answer.