You could say "DO IT, YOU IDIOT! " but you know... with a smile on your face :-p Just kidding! Juan Luis is right! Now, what about adding the magic word PLEASE, it goes like this "Would you please be so kind as to do something for me?? " (whatever it is that you need) It always works ! :)

Hi, I would say: WOULD you be so kind as to... (...do this)? (this one is very formal and polite). The second expression you propose should be written: "COULD" The fourth (WOUID) does not exist.

Often it isn't which one of these that you use but the words you use with them. Can you do this? Could you do this? Would you do this? - These are fairly neutral but can sound impolite. Adding please - "Could you please do this?" (This is polite if asked nicely) Other things you could add: Would you mind doing this? (This is informal and polite if asked nicely) I'd appreciate it if you could do this please? (This is very polite) Can you maybe do this for me? (Adding the maybe makes you sound like you don't want to bother the other person, it's casual and fairly polite) If you wouldn't mind (could/would/can) you do this please? (Very polite) Most of these can be used in almost any situation. Normally if you just ask with a friendly tone of voice people will assume you are being polite, though a lot of people prefer you at least say please. :)

In truth, you should know when to use any of these expressions, and not always resort to the "most polite" one.

It really depends on what you're asking, and how you ask it. All of the words you provided have varying meanings, so I'll detail the slight differences. 1] can you: This one is asking if the person is physically, or otherwise capable of performing your request. This one is the least formal because it could imply that you believe the person is unable to perform a simple task. A:"Can you open the door?" B:"No, I'm paraplegic, and therefore cannot." 2] could you: This is also similar to "can", but it's a little more formal. Unlike "can", however, "could" is asking basically if there is a possibility that the person would perform your request. A:"Could you open the door, please?" B:"I could, but I won't " 3] would you: Is basically the most polite word to use, because it's very indirect. This is the past tense of "will", and can be used interchangeably with it in most instances. A:"Would you be a dear, and fetch me the paper?" B:"I would, if only you would say please, you heathen!" 4] should you: I'm assuming you meant to write "should". This one implies that there is a decision to make about whether or not something is a necessary course of action. Something that should be done is something that needs to happen. A:"Should I go to work today?" B:"No way, money is the root of all evil" Hope that helps.