POLITE EXPRESSIONS.

EXCUSE ME

You say excuse me when you want to go past somebody.

You also say excuse me to somebody you do not know when you want to attract their attention.

Ex. Excuse me, is anyone sitting here?

SORRY

I beg your pardon is a formal expression when you need to apologize for something.

Ex. I beg your pardon! I must have picked up the wrong bag by mistake.

Sorry or I'm sorry is used frequently in British English, and in American English Pardon me and excuse me are used for apologies.

In British English you say Pardon? or Sorry? And in American English Pardon me? And Excuse me? When you did not hear or understand what somebody said and want them to repeat it.

It is not polite to say What? in that situations.

I'M AFRAID

You use the phrase I'm afraid... when you want to apologize because you have to tell somebody something that they may not like.

Ex.  -'Has the last bus gone?' - 'I`m afraid so'

I`m afraid there's been an accident.

I WONDER IF...

You use expressions which show hesitancy when you are asking for a favor:

Could you just help me move these boxes, please?

I wonder if I could have a copy of your paper?

Would you mind if I left a few minutes early today?

Would you mind letting me leave the class at 12?

Do you think I could borrow your car this weekend?

PLEASE

You say please when you ask for something. In British English it introduces or ends a request, but in American English it always ends a request.

Please could I have the menu?

Could I have the menu please?

THANK YOU

When somebody gives you something, or when you buy something or receive information, you are expected to say Thank you or Thanks.

It is not usual to say anything in response to Thank you in British English, although some people may say That's all right, That's okay or Don't mention it.

In American English You’re welcome is common. 

CHEERS

Cheers is often used in informal British English to mean Thank you.

ex.: -'here's that 10 Euros I owe you'  - ' oh, cheers'