On my polite-o-meter, the two sentences score very close: "Could you help me, please?", "Could you please help me?". The former sounds more formal. Use whichever one you want and you'll be more polite than most people.
The following data is a very rough indication that "please-on-the-end" might be more common: 1
1 Google results may not be accurate at all. I will be reviewing this. Another answer suggests a different result.
Sentence structure has an impact on information emphasis:
Sentence length tends to require "please" to be moved to the beginning. Consider the following: "Could you help me find my light-brown work shoes that I just bought, please?" "Could you please help me find my light-brown work shoes that I just bought?" The latter introduces politeness earlier while also focusing the sentence on the important information.
Other answers in this thread provide great analyses on formality and urgency. But length-of-sentence can be an opposing force. While "please" tends to be more formal and polite at the end of sentences, a longer sentence may be more natural sounding with "please" moved closer to the beginning. For more information, see Google Search: sentence information, clarity, and focus.
How to learn all of this?
- There are a lot of great answers in this thread (I suggest you read them too!), but that can be overwhelming! Usage is highly dependent on context. Rather than trying to learn 1000 rules on usage, I suggest that you gain subtle usage skills naturally through observation and experience .
Are you sure the name isn't supposed to be Janet Wayne? It's strange to say "My friends call me Jan" when that's her actual first name. Normally that pattern is used for abbreviations or nicknames, but people would call her Jan by default.
In general, I suggest not using "My friends call me X". It's not always clear whether the person you're speaking to counts as a friend or wants to be a friend. Context, can help, but some people (like me) find it a bit intimidating. You can use "You can call me X" or "I go by X" instead. This is just my opinion; the phrase is definitely correct idiomatic English.
I don't think the first sentence is necessarily informal in the sense of being potentially rude. For instance, if you were meeting the CEO of an American company face to face, it would be fine. Still, there are some changes you can make to fit various circumstances.
When addressing a group, as in a lecture or presentation, it helps to add a few syllables to make your words easier to hear:
Hello, everyone! My name is Janet Wayne. You can call me Jan.
Alternately, you can just use the abbreviated name to begin with:
Hello, everyone! My name is Jan Wayne.
When meeting someone face to face, you can add an extra sentence:
Hi! My name's Jan. It's nice to meet you.
Saying "It's nice to meet you" will make more of an impression than the grammar you use.
Formality depends as much on culture as it does on language. You might get a better answer if you tell us who you're introducing yourself to. Americans? Brits? Australians?
UPDATE: In the question, you asked about introducing yourself. If you tell someone "My name is Jan Wayne", they'll call you Jan. You don't need to say "My friends call me Jan". What else would they call you? "My friends call me X" is normally only used with shortened names and nicknames. You could also use it to ask someone to call you Jan instead of Ms. Wayne, but that's less common.
If your legal name is different from what people call you, then it makes sense:
My name is Elizabeth Taylor. You can call me Liz.
My name is Theodore Olson. I go by Ted.
My name is Janet Wayne. My friends call me Jan.
Sometimes people use their middle name instead of their first name:
My name is Walter Bruce Willis. You can call me Bruce.
or:
My name is Walter Willis; I go by Bruce.
But it would be weird to say:
My name is Adam Haun. I go by Adam.
Best Answer
While you can do things with good manners, it is rare to direct someone to do so in imperatives. Unless addressing children, it is not required to remind people to be polite— a person with good upbringing has good manners out of habit; an poorly raised person cannot tell the difference, anyway.
This may reflect a difference of cultural perception, but I think more likely that it is simply a poor translation from Japanese. A search on "smoke with good manners" mostly returns results from Japan. Considerate would be the more idiomatic adjective to use to remind people to think of others, so a similar campaign in an English-speaking city might be please be a considerate smoker or please be considerate when smoking, phrasings which are common in such signs.
When speaking generally of politeness, consideration, and other positive social behavior, good manners are something you have, not something you do (as with one's habits or one's nature). Someone with good manners may be said to be well-mannered, and someone without good manners is ill-mannered; it is more usually expressed that someone has good manners, than that they do something with good manners.